A081811 If n = p_1^e_1 * ... * p_k^e_k, p_1 < ... < p_k primes, then a(n) = min{ p_i*e_i }.

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, 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, 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

Offset: 1

Author

Benoit Cloitre, Apr 10 2003

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A081810 (with max).

Programs

Maple

a:= n-> `if`(n=1, 0, min(seq(i[1]*i[2], i=ifactors(n)[2]))):
seq(a(n), n=1..100);  # Alois P. Heinz, Jul 19 2020

Mathematica

a[n_] := If[n == 1, 0, Min[Times @@@ FactorInteger[n]]];
Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Jan 13 2025 *)

PARI

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