A163751 a(n) = n-th even nonprime minus n-th nonprime.

0, 3, 2, 2, 2, 3, 4, 4, 4, 5, 6, 6, 6, 7, 8, 8, 9, 10, 11, 12, 12, 12, 13, 14, 15, 16, 16, 17, 18, 18, 18, 19, 20, 20, 21, 22, 23, 24, 24, 25, 26, 27, 28, 28, 28, 29, 30, 31, 32, 32, 33, 34, 34, 34, 35, 36, 37, 38, 38, 39, 40, 40, 41, 42, 43, 44, 44, 45, 46, 47, 48, 49, 50, 50, 51

Offset: 1

Author

Juri-Stepan Gerasimov, Aug 03 2009

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A141468, A163300.

Programs

Mathematica

nonPrime[n_Integer] := FixedPoint[n + PrimePi@# &, n + PrimePi@n];
A087156[n_] := Mod[n, DivisorSigma[1, n]]; A141468 := Array[nonPrime, 60, 0]; Table[2*A087156[n] - A141468[[n]], {n, 1, 50}] (* G. C. Greubel, Aug 02 2017 *)

Formula

a(n) = (A163300(n) - A141468(n)).

Extensions

Entries checked by R. J. Mathar, May 21 2010