A171576 a(n) = abs(n-th noncomposite number minus n-th even nonprime number).

1, 2, 3, 3, 3, 1, 1, 1, 1, 3, 7, 7, 11, 13, 13, 15, 19, 23, 23, 27, 29, 29, 33, 35, 39, 45, 47, 47, 49, 49, 51, 63, 65, 69, 69, 77, 77, 81, 85, 87, 91, 95, 95, 103, 103, 105, 105, 115, 125, 127, 127, 129, 133, 133, 141, 145, 149, 153, 153, 157, 159, 159, 167, 179, 181

Offset: 1

Author

Juri-Stepan Gerasimov, Dec 12 2009

Keywords

• nonn

Examples

			a(1) = abs(1-0) = 1, a(2) = abs(2-4) = 2, a(3) = abs(3-6) = 3.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A008578 (noncomposite), A163300 (even nonprime).

Programs

Mathematica

Module[{nn=400,nc,enp,len},nc=Select[Range[nn],!CompositeQ[#]&];enp= Join[{0},Range[4,nn,2]];len=Min[Length[nc],Length[enp]];Abs[#[[1]]- #[[2]]]&/@Thread[{Take[nc,len],Take[enp,len]}]] (* Harvey P. Dale, Mar 01 2020 *)

Formula

a(n) = abs(A008578(n) - A163300(n)).

Extensions

Corrected (a 67 replaced by another 69) by R. J. Mathar, May 22 2010