A176569 a(n) = (-1)^n + (n-th prime of the form 3k-+1).

1, 6, 6, 12, 12, 18, 18, 24, 28, 32, 36, 42, 42, 48, 52, 60, 60, 68, 70, 74, 78, 84, 88, 98, 100, 104, 106, 110, 112, 128, 130, 138, 138, 150, 150, 158, 162, 168, 172, 180, 180, 192, 192, 198, 198, 212, 222, 228, 228, 234, 238, 242, 250, 258, 262, 270, 270, 278

Offset: 1

Author

Juri-Stepan Gerasimov, Apr 20 2010

Keywords

• nonn

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10001

Crossrefs

Cf. A045344.

Programs

Maple

A045344 := proc(n) if n = 1 then 2; else ithprime(n+1) ; end if; end proc:
A176569 := proc(n) (-1)^n+A045344(n) ; end proc:
seq(A176569(n),n=1..120) ; # R. J. Mathar, Apr 27 2010

Mathematica

Total /@ Nest[Append[#1, Block[{p = NextPrime@ #1[[-1, -1]]}, While[Mod[p, 3] == 0, p = NextPrime@ p]; {(-1)^#2, p}]] & @@ {#, Length@ # + 1} &, {{-1, 2}}, 57] (* Michael De Vlieger, Feb 09 2019 *)

PARI

a045344(n) = if(n<2, 2, prime(n+1));
a(n) = (-1)^n + a045344(n); \\ Michel Marcus, Feb 07 2019

Formula

a(n) = (-1)^n + A045344(n). - Michel Marcus, Feb 07 2019

Extensions

Corrected (double-5 replaced by double-6, 146 removed) by R. J. Mathar, Apr 27 2010