A074828 a(1) = 1; for n>1, a(n) = smallest composite multiple of n if n is a prime else the smallest prime divisor of n if n is composite.

1, 4, 6, 2, 10, 2, 14, 2, 3, 2, 22, 2, 26, 2, 3, 2, 34, 2, 38, 2, 3, 2, 46, 2, 5, 2, 3, 2, 58, 2, 62, 2, 3, 2, 5, 2, 74, 2, 3, 2, 82, 2, 86, 2, 3, 2, 94, 2, 7, 2, 3, 2, 106, 2, 5, 2, 3, 2, 118, 2, 122, 2, 3, 2, 5, 2, 134, 2, 3, 2, 142, 2, 146, 2, 3, 2, 7, 2, 158, 2, 3, 2, 166, 2, 5, 2, 3, 2, 178, 2

Offset

1,2

Comments

a(n) = 2n if n is a prime, a(2n+2) = 2.

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

Prog

(PARI) print1("1, "); for(n=2, 100, if(isprime(n), print1(2*n, ", "), print1(factor(n)[1, 1], ", "))) (Rick L. Shepherd)
(PARI) A074828(n) = if(1==n, n, if(isprime(n), 2*n, factor(n)[1, 1])); \\ Antti Karttunen, Feb 06 2019

Crossrefs

Cf. A020639.

Sequence in context: A021220 A195410 A095196 * A282028 A251561 A159193

Adjacent sequences: A074825 A074826 A074827 * A074829 A074830 A074831

Keyword

nonn

Author

Amarnath Murthy, Sep 13 2002

Extensions

More terms from Rick L. Shepherd, Jun 07 2004

Entry revised by N. J. A. Sloane, Aug 13 2006

Status

approved