A081811 - OEIS

%I #13 Jul 19 2020 10:14:32

%S 0,2,3,4,5,2,7,6,6,2,11,3,13,2,3,8,17,2,19,4,3,2,23,3,10,2,9,4,29,2,

%T 31,10,3,2,5,4,37,2,3,5,41,2,43,4,5,2,47,3,14,2,3,4,53,2,5,6,3,2,59,3,

%U 61,2,6,12,5,2,67,4,3,2,71,6,73,2,3,4,7,2,79,5,12,2,83,3,5,2,3,6,89,2,7,4,3

%N If n = p_1^e_1 * ... * p_k^e_k, p_1 < ... < p_k primes, then a(n) = min{ p_i*e_i }.

%H Alois P. Heinz, <a href="/A081811/b081811.txt">Table of n, a(n) for n = 1..10000</a>

%p a:= n-> `if`(n=1, 0, min(seq(i[1]*i[2], i=ifactors(n)[2]))):

%p seq(a(n), n=1..100);  # _Alois P. Heinz_, Jul 19 2020

%o (PARI) a(n)=local(f); if(n==1,0,f=factor(n); vecmin(vector(matsize(f)[1],k,f[k,1]*f[k,2])))

%Y Cf. A081810 (with max).

%K nonn

%O 1,2

%A _Benoit Cloitre_, Apr 10 2003