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

1,2

Links

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

Formula

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

Example

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

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 *)

Crossrefs

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

Sequence in context: A118925 A308100 A351065 * A016738 A061911 A328397

Adjacent sequences: A171573 A171574 A171575 * A171577 A171578 A171579

Keyword

nonn

Author

Juri-Stepan Gerasimov, Dec 12 2009

Extensions

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

Status

approved