|
%I #9 Jun 27 2013 13:55:51
%S 2,2,2,2,5,5,2,2,7,7,3,3,2,2,2,2,5,5,11,3,2,2,7,7,2,2,2,2,5,5,2,2,3,3,
%T 3,3,2,2,5,5,2,2,2,2,3,3,13,13,2,2,2,2,17,5,2,2,3,3,7,7,2,2,2,2,3,3,3,
%U 5,2,2,7,7,2,2,2,2,11
%N a(n) is the smallest prime occurring in the prime factorization of n! to an odd power.
%C If n is even then a(n) is also the smallest prime factor in the binomial coefficient C(n, n/2).
%H Charles R Greathouse IV, <a href="/A118486/b118486.txt">Table of n, a(n) for n = 2..10000</a>
%e a(10) = 7 since 10! = 2^8 * 3^4 * 5^2 * 7 * 11.
%o (PARI) a(n) = f = factor(n!); for (i=1, #f~, if (f[i,2] % 2, return (f[i, 1]))); \\ _Michel Marcus_, Jun 27 2013
%o (PARI) valp(n,p)=my(s);while(n\=p,s+=n);s
%o a(n)=forprime(p=2,,if(valp(n,p)%2,return(p))) \\ _Charles R Greathouse IV_, Jun 27 2013
%K nonn
%O 2,1
%A _John L. Drost_, Jul 21 2007
|
