A161843 a(n) = n-th composite plus n-th nonprime.

4, 7, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 47, 50, 52, 54, 57, 60, 63, 66, 68, 70, 73, 75, 78, 81, 84, 87, 90, 93, 95, 98, 100, 102, 105, 107, 110, 112, 114, 117, 120, 123, 126, 128, 130, 133, 135, 138, 141, 144, 147, 150, 152, 154, 157, 159, 162, 165, 167

Offset

1,1

Links

Table of n, a(n) for n=1..61.

Formula

a(n) = A002808(n) + A141468(n).

Example

4(=4+0), 7(=6+1), 12(=8+4), 15(=9+6), 18(=10+8), 21(=12+9), etc.

Mathematica

Module[{comps=Select[Range[100], CompositeQ]}, Total/@Thread[{Join[ {0, 1}, Most[ Most[comps]]], comps}]] (* Harvey P. Dale, Aug 11 2014 *)

Crossrefs

Cf. A002808, A141468.

Sequence in context: A244590 A310770 A268816 * A085048 A024813 A276880

Adjacent sequences: A161840 A161841 A161842 * A161844 A161845 A161846

Keyword

nonn

Author

Juri-Stepan Gerasimov, Jun 20 2009

Extensions

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

Status

approved