A107286 a(0) = 0; for n>0, minimal prime factor of n, or 1 if n is 1 or a prime.

0, 1, 1, 1, 2, 1, 2, 1, 2, 3, 2, 1, 2, 1, 2, 3, 2, 1, 2, 1, 2, 3, 2, 1, 2, 5, 2, 3, 2, 1, 2, 1, 2, 3, 2, 5, 2, 1, 2, 3, 2, 1, 2, 1, 2, 3, 2, 1, 2, 7, 2, 3, 2, 1, 2, 5, 2, 3, 2, 1, 2, 1, 2, 3, 2, 5, 2, 1, 2, 3, 2, 1, 2, 1, 2, 3, 2, 7, 2, 1, 2, 3, 2, 1, 2, 5, 2, 3, 2, 1, 2, 7, 2, 3, 2, 5, 2, 1, 2, 3

Offset: 0

Author

Giovanni Teofilatto, May 20 2005

Keywords

• nonn
• look

Links

• Antti Karttunen, Table of n, a(n) for n = 0..20000

Crossrefs

Cf. A020639.

Programs

PARI

a(n) = if (n==0, 0, if (n==1, 1, if (isprime(n), 1, factor(n)[1,1]))) \\ Michel Marcus, Jun 03 2013