cp's OEIS Frontend

A378157 The least prime dividing !n = A000166(n).

%I A378157 #12 Jun 21 2025 19:59:08
%S A378157 2,3,2,5,2,7,2,3,2,11,2,13,2,3,2,17,2,11,2,3,2,23,2,5,2,3,2,29,2,31,2,
%T A378157 3,2,5,2,11,2,3,2,11,2,43,2,3,2,47,2,7,2,3,2,53,2,5,2,3,2,11,2,61,2,3,
%U A378157 2,5,2,67,2,3,2,71,2,73,2,3,2,7,2,79,2,3,2
%N A378157 The least prime dividing !n = A000166(n).
%H A378157 Amiram Eldar, <a href="/A378157/b378157.txt">Table of n, a(n) for n = 3..10000</a>
%F A378157 a(n) = A020639(A000166(n)).
%F A378157 a(n) = min(A020639(n-1), A378159(n-2)) for n >= 2.
%t A378157 lpf[n_] := Module[{p = 2}, While[! Divisible[n, p], p = NextPrime[p]]; p]; Array[lpf[Subfactorial[#]] &, 50, 3]
%o A378157 (PARI) lpf(n) = {my(p = 2); while(n % p, p = nextprime(p+1)); p;}
%o A378157 lista(nmax) = {my(s = 1); for(n = 3, nmax, s = n * s + (-1)^n; print1(lpf(s), ", ")); }
%Y A378157 Cf. A000166, A020639, A152024, A195207, A195208, A195209, A195210, A378158, A378159.
%K A378157 nonn
%O A378157 3,1
%A A378157 _Amiram Eldar_, Nov 18 2024