facnn2 - Metamath Proof Explorer

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Theorem facnn2 13391

Description: Value of the factorial function expressed recursively. (Contributed by NM, 2-Dec-2004.)

**Assertion**
Ref	Expression
facnn2	⊢ (𝑁 ∈ ℕ → (!‘𝑁) = ((!‘(𝑁 − 1)) · 𝑁))

**Proof of Theorem facnn2**
Step	Hyp	Ref	Expression
1		elnnnn0 11691	. 2 ⊢ (𝑁 ∈ ℕ ↔ (𝑁 ∈ ℂ ∧ (𝑁 − 1) ∈ ℕ₀))
2		facp1 13387	. . . 4 ⊢ ((𝑁 − 1) ∈ ℕ₀ → (!‘((𝑁 − 1) + 1)) = ((!‘(𝑁 − 1)) · ((𝑁 − 1) + 1)))
3	2	adantl 475	. . 3 ⊢ ((𝑁 ∈ ℂ ∧ (𝑁 − 1) ∈ ℕ₀) → (!‘((𝑁 − 1) + 1)) = ((!‘(𝑁 − 1)) · ((𝑁 − 1) + 1)))
4		npcan1 10802	. . . . 5 ⊢ (𝑁 ∈ ℂ → ((𝑁 − 1) + 1) = 𝑁)
5	4	fveq2d 6452	. . . 4 ⊢ (𝑁 ∈ ℂ → (!‘((𝑁 − 1) + 1)) = (!‘𝑁))
6	5	adantr 474	. . 3 ⊢ ((𝑁 ∈ ℂ ∧ (𝑁 − 1) ∈ ℕ₀) → (!‘((𝑁 − 1) + 1)) = (!‘𝑁))
7	4	oveq2d 6940	. . . 4 ⊢ (𝑁 ∈ ℂ → ((!‘(𝑁 − 1)) · ((𝑁 − 1) + 1)) = ((!‘(𝑁 − 1)) · 𝑁))
8	7	adantr 474	. . 3 ⊢ ((𝑁 ∈ ℂ ∧ (𝑁 − 1) ∈ ℕ₀) → ((!‘(𝑁 − 1)) · ((𝑁 − 1) + 1)) = ((!‘(𝑁 − 1)) · 𝑁))
9	3, 6, 8	3eqtr3d 2822	. 2 ⊢ ((𝑁 ∈ ℂ ∧ (𝑁 − 1) ∈ ℕ₀) → (!‘𝑁) = ((!‘(𝑁 − 1)) · 𝑁))
10	1, 9	sylbi 209	1 ⊢ (𝑁 ∈ ℕ → (!‘𝑁) = ((!‘(𝑁 − 1)) · 𝑁))

Colors of variables: wff setvar class

Syntax hints: → wi 4 ∧ wa 386 = wceq 1601 ∈ wcel 2107 ‘cfv 6137 (class class class)co 6924 ℂcc 10272 1c1 10275 + caddc 10277 · cmul 10279 − cmin 10608 ℕcn 11378 ℕ₀cn0 11646 !cfa 13382

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1839 ax-4 1853 ax-5 1953 ax-6 2021 ax-7 2055 ax-8 2109 ax-9 2116 ax-10 2135 ax-11 2150 ax-12 2163 ax-13 2334 ax-ext 2754 ax-sep 5019 ax-nul 5027 ax-pow 5079 ax-pr 5140 ax-un 7228 ax-cnex 10330 ax-resscn 10331 ax-1cn 10332 ax-icn 10333 ax-addcl 10334 ax-addrcl 10335 ax-mulcl 10336 ax-mulrcl 10337 ax-mulcom 10338 ax-addass 10339 ax-mulass 10340 ax-distr 10341 ax-i2m1 10342 ax-1ne0 10343 ax-1rid 10344 ax-rnegex 10345 ax-rrecex 10346 ax-cnre 10347 ax-pre-lttri 10348 ax-pre-lttrn 10349 ax-pre-ltadd 10350 ax-pre-mulgt0 10351

This theorem depends on definitions: df-bi 199 df-an 387 df-or 837 df-3or 1072 df-3an 1073 df-tru 1605 df-ex 1824 df-nf 1828 df-sb 2012 df-mo 2551 df-eu 2587 df-clab 2764 df-cleq 2770 df-clel 2774 df-nfc 2921 df-ne 2970 df-nel 3076 df-ral 3095 df-rex 3096 df-reu 3097 df-rab 3099 df-v 3400 df-sbc 3653 df-csb 3752 df-dif 3795 df-un 3797 df-in 3799 df-ss 3806 df-pss 3808 df-nul 4142 df-if 4308 df-pw 4381 df-sn 4399 df-pr 4401 df-tp 4403 df-op 4405 df-uni 4674 df-iun 4757 df-br 4889 df-opab 4951 df-mpt 4968 df-tr 4990 df-id 5263 df-eprel 5268 df-po 5276 df-so 5277 df-fr 5316 df-we 5318 df-xp 5363 df-rel 5364 df-cnv 5365 df-co 5366 df-dm 5367 df-rn 5368 df-res 5369 df-ima 5370 df-pred 5935 df-ord 5981 df-on 5982 df-lim 5983 df-suc 5984 df-iota 6101 df-fun 6139 df-fn 6140 df-f 6141 df-f1 6142 df-fo 6143 df-f1o 6144 df-fv 6145 df-riota 6885 df-ov 6927 df-oprab 6928 df-mpt2 6929 df-om 7346 df-2nd 7448 df-wrecs 7691 df-recs 7753 df-rdg 7791 df-er 8028 df-en 8244 df-dom 8245 df-sdom 8246 df-pnf 10415 df-mnf 10416 df-xr 10417 df-ltxr 10418 df-le 10419 df-sub 10610 df-neg 10611 df-nn 11379 df-n0 11647 df-z 11733 df-uz 11997 df-seq 13124 df-fac 13383

This theorem is referenced by: faclbnd4lem1 13402 bcn1 13422 bcm1k 13424 hashf1 13559 dvdsfac 15459 chtublem 25392 bcmono 25458 dvnxpaek 41095

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