A117668 a(n) is the n-th prime number if n is prime; a(n) is the n-th nonprime number otherwise.

1, 3, 5, 8, 11, 10, 17, 14, 15, 16, 31, 20, 41, 22, 24, 25, 59, 27, 67, 30, 32, 33, 83, 35, 36, 38, 39, 40, 109, 44, 127, 46, 48, 49, 50, 51, 157, 54, 55, 56, 179, 58, 191, 62, 63, 64, 211, 66, 68, 69, 70, 72, 241, 75, 76, 77, 78, 80, 277, 82, 283, 85, 86, 87, 88, 90, 331, 92, 93, 94, 353, 96, 367, 99, 100

Offset

1,2

Links

Table of n, a(n) for n=1..75.

Example

a(1) is the first nonprime: 1.
a(2) is the second prime: 3.

Mathematica

Module[{nn=100, np, pr, len}, np=Select[Range[nn], !PrimeQ[#]&]; len = Length[ np]; pr=Prime[Range[len]]; Table[If[PrimeQ[n], pr[[n]], np[[n]]], {n, len}]] (* Harvey P. Dale, Oct 01 2021 *)

Crossrefs

Cf. A000040, A002808.

Sequence in context: A127700 A101907 A242250 * A184410 A184332 A326711

Adjacent sequences: A117665 A117666 A117667 * A117669 A117670 A117671

Keyword

nonn

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 11 2006

Extensions

Definition corrected by Michel Marcus, Jun 01 2013

Corrected and extended by Harvey P. Dale, Oct 01 2021

Status

approved