A089993 Penultimate prime divisor of numbers that are not powers of primes (A024619).

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

Amiram Eldar, Table of n, a(n) for n = 1..10000

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

Cf. A024619, A076820, A089992.

Sequence in context: A324538 A305976 A074592 * A220431 A351284 A268317

Adjacent sequences: A089990 A089991 A089992 * A089994 A089995 A089996

Keyword

nonn

Author

Cino Hilliard, Jan 14 2004

Extensions

Offset corrected by Amiram Eldar, Apr 12 2021

Status

approved