A066560 Smallest composite number divisible by n.

4, 4, 6, 4, 10, 6, 14, 8, 9, 10, 22, 12, 26, 14, 15, 16, 34, 18, 38, 20, 21, 22, 46, 24, 25, 26, 27, 28, 58, 30, 62, 32, 33, 34, 35, 36, 74, 38, 39, 40, 82, 42, 86, 44, 45, 46, 94, 48, 49, 50, 51, 52, 106, 54, 55, 56, 57, 58, 118, 60, 122, 62, 63, 64, 65, 66, 134, 68, 69, 70

Offset: 1

Author

Amarnath Murthy, Dec 17 2001

Keywords

• nonn

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Programs

PARI

a(n) = { if(n==1, 4, if(isprime(n), 2*n, n)) } \\ Harry J. Smith, Mar 02 2010

Formula

For n>=2: a(n) = 2*n if n prime; otherwise a(n) = n.

Extensions

More terms and formula from Francisco Salinas (franciscodesalinas(AT)hotmail.com), Dec 24 2001