login
A089993
Penultimate prime divisor of numbers that are not powers of primes (A024619).
2
2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 2, 3, 3, 2, 5, 2, 2, 3, 2, 3, 2, 3, 2, 2, 2, 3, 2, 2, 5, 2, 3, 2, 3, 2, 3, 5, 3, 2, 3, 5, 2, 2, 3, 2, 7, 3, 2, 2, 3, 5, 2, 3, 2, 3, 7, 2, 3, 2, 5, 2, 2, 3, 2, 3, 2, 5, 2, 2, 5, 3, 2, 3, 5, 2, 3, 2, 7, 3, 2, 3, 2, 3, 3, 5, 3, 7, 2, 3, 2, 3, 5, 3, 2, 11, 2, 5, 2, 3, 2, 3, 2, 3, 7, 5
OFFSET
1,1
LINKS
FORMULA
a(n) = A076820(A024619(n)). - Amiram Eldar, Apr 12 2021
MATHEMATICA
Select[Table[If[Length[(f = FactorInteger[n])] > 1, f[[-2, 1]], 1], {n, 1, 150}], # > 1 &]
PROG
(PARI) f(n) = a=factor(n); v=a[, 1]; ln=length(v); if(ln>1, return(v[ln-1]));
g(m) = for(x=2, m, if(f(x)>0, print1(f(x)", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Cino Hilliard, Jan 14 2004
EXTENSIONS
Offset corrected by Amiram Eldar, Apr 12 2021
STATUS
approved