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Mirrors > Home > ILE Home > Th. List > mulsucdiv2z | GIF version |
Description: An integer multiplied with its successor divided by 2 yields an integer, i.e. an integer multiplied with its successor is even. (Contributed by AV, 19-Jul-2021.) |
Ref | Expression |
---|---|
mulsucdiv2z | ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | zeo 9383 | . 2 ⊢ (𝑁 ∈ ℤ → ((𝑁 / 2) ∈ ℤ ∨ ((𝑁 + 1) / 2) ∈ ℤ)) | |
2 | peano2z 9314 | . . . . . 6 ⊢ (𝑁 ∈ ℤ → (𝑁 + 1) ∈ ℤ) | |
3 | zmulcl 9331 | . . . . . 6 ⊢ (((𝑁 / 2) ∈ ℤ ∧ (𝑁 + 1) ∈ ℤ) → ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ) | |
4 | 2, 3 | sylan2 286 | . . . . 5 ⊢ (((𝑁 / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ) |
5 | zcn 9283 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → 𝑁 ∈ ℂ) | |
6 | 2 | zcnd 9401 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → (𝑁 + 1) ∈ ℂ) |
7 | 2cnd 9017 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → 2 ∈ ℂ) | |
8 | 2ap0 9037 | . . . . . . . . 9 ⊢ 2 # 0 | |
9 | 8 | a1i 9 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → 2 # 0) |
10 | 5, 6, 7, 9 | div23apd 8810 | . . . . . . 7 ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) = ((𝑁 / 2) · (𝑁 + 1))) |
11 | 10 | eleq1d 2258 | . . . . . 6 ⊢ (𝑁 ∈ ℤ → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ)) |
12 | 11 | adantl 277 | . . . . 5 ⊢ (((𝑁 / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ)) |
13 | 4, 12 | mpbird 167 | . . . 4 ⊢ (((𝑁 / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
14 | 13 | ex 115 | . . 3 ⊢ ((𝑁 / 2) ∈ ℤ → (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ)) |
15 | zmulcl 9331 | . . . . . 6 ⊢ ((𝑁 ∈ ℤ ∧ ((𝑁 + 1) / 2) ∈ ℤ) → (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ) | |
16 | 15 | ancoms 268 | . . . . 5 ⊢ ((((𝑁 + 1) / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ) |
17 | 5, 6, 7, 9 | divassapd 8808 | . . . . . . 7 ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) = (𝑁 · ((𝑁 + 1) / 2))) |
18 | 17 | eleq1d 2258 | . . . . . 6 ⊢ (𝑁 ∈ ℤ → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ)) |
19 | 18 | adantl 277 | . . . . 5 ⊢ ((((𝑁 + 1) / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ)) |
20 | 16, 19 | mpbird 167 | . . . 4 ⊢ ((((𝑁 + 1) / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
21 | 20 | ex 115 | . . 3 ⊢ (((𝑁 + 1) / 2) ∈ ℤ → (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ)) |
22 | 14, 21 | jaoi 717 | . 2 ⊢ (((𝑁 / 2) ∈ ℤ ∨ ((𝑁 + 1) / 2) ∈ ℤ) → (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ)) |
23 | 1, 22 | mpcom 36 | 1 ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 104 ↔ wb 105 ∨ wo 709 ∈ wcel 2160 class class class wbr 4018 (class class class)co 5892 0cc0 7836 1c1 7837 + caddc 7839 · cmul 7841 # cap 8563 / cdiv 8654 2c2 8995 ℤcz 9278 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia1 106 ax-ia2 107 ax-ia3 108 ax-in1 615 ax-in2 616 ax-io 710 ax-5 1458 ax-7 1459 ax-gen 1460 ax-ie1 1504 ax-ie2 1505 ax-8 1515 ax-10 1516 ax-11 1517 ax-i12 1518 ax-bndl 1520 ax-4 1521 ax-17 1537 ax-i9 1541 ax-ial 1545 ax-i5r 1546 ax-13 2162 ax-14 2163 ax-ext 2171 ax-sep 4136 ax-pow 4189 ax-pr 4224 ax-un 4448 ax-setind 4551 ax-cnex 7927 ax-resscn 7928 ax-1cn 7929 ax-1re 7930 ax-icn 7931 ax-addcl 7932 ax-addrcl 7933 ax-mulcl 7934 ax-mulrcl 7935 ax-addcom 7936 ax-mulcom 7937 ax-addass 7938 ax-mulass 7939 ax-distr 7940 ax-i2m1 7941 ax-0lt1 7942 ax-1rid 7943 ax-0id 7944 ax-rnegex 7945 ax-precex 7946 ax-cnre 7947 ax-pre-ltirr 7948 ax-pre-ltwlin 7949 ax-pre-lttrn 7950 ax-pre-apti 7951 ax-pre-ltadd 7952 ax-pre-mulgt0 7953 ax-pre-mulext 7954 |
This theorem depends on definitions: df-bi 117 df-3or 981 df-3an 982 df-tru 1367 df-fal 1370 df-nf 1472 df-sb 1774 df-eu 2041 df-mo 2042 df-clab 2176 df-cleq 2182 df-clel 2185 df-nfc 2321 df-ne 2361 df-nel 2456 df-ral 2473 df-rex 2474 df-reu 2475 df-rmo 2476 df-rab 2477 df-v 2754 df-sbc 2978 df-dif 3146 df-un 3148 df-in 3150 df-ss 3157 df-pw 3592 df-sn 3613 df-pr 3614 df-op 3616 df-uni 3825 df-int 3860 df-br 4019 df-opab 4080 df-id 4308 df-po 4311 df-iso 4312 df-xp 4647 df-rel 4648 df-cnv 4649 df-co 4650 df-dm 4651 df-iota 5193 df-fun 5234 df-fv 5240 df-riota 5848 df-ov 5895 df-oprab 5896 df-mpo 5897 df-pnf 8019 df-mnf 8020 df-xr 8021 df-ltxr 8022 df-le 8023 df-sub 8155 df-neg 8156 df-reap 8557 df-ap 8564 df-div 8655 df-inn 8945 df-2 9003 df-n0 9202 df-z 9279 |
This theorem is referenced by: sqoddm1div8z 11918 |
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