A163578 If n is prime, a(n) is next composite greater than a(n-1), else if n is composite, a(n) is next prime greater than a(n-1) else 2.

2, 4, 6, 7, 8, 11, 12, 13, 17, 19, 20, 23, 24, 29, 31, 37, 38, 41, 42, 43

Offset

1,1

Links

Table of n, a(n) for n=1..20.

Example

1 is not prime, a(1)=2, 2 is prime, a(2)=4, 3 is prime, a(3)=6, 4 is composite, a(4)=7.

Crossrefs

Cf. A159559

Sequence in context: A165778 A286066 A139527 * A345918 A269389 A092054

Adjacent sequences: A163575 A163576 A163577 * A163579 A163580 A163581

Keyword

nonn

Author

Gerald Hillier, Jul 31 2009

Status

approved