A249224 - OEIS

%I #9 Oct 27 2014 05:32:36

%S 2,13,3,2,2,3,3,2,2,3,11,2,2,5,3,2,2,3,3,2,2,3,17,2,2,13,3,2,2,3,3,2,

%T 2,3,5,2,2,7,3,2,2,3,3,2,2,3,29,2,2,5,3,2,2,3,3,2,2,3,5,2,2,31,3,2,2,

%U 3,3,2,2,3,41,2,2,5,3,2,2,3,3,2,2,3,47,2,2,43,3,2,2,3,3,2,2,3,5,2,2,7,3,2

%N Lpf (n(n+11)/2): least prime dividing n(n+11)/2.

%C a(n) = 2 for n = {4,5,8,9} (mod 12) and a(n) = 3 for n = {3,6,7,10} (mod 12).

%H Zak Seidov, <a href="/A249224/b249224.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A020639(n(n+11)/2).

%t FactorInteger[#(11+#)/2][[1,1]]& /@ Range[100]

%o (PARI) a(n) = my(f=factor(n*(n+11)/2)); f[1,1]; \\ _Michel Marcus_, Oct 23 2014

%Y Cf. A056115, A020639.

%K nonn,easy

%O 1,1

%A _Zak Seidov_, Oct 23 2014