Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #10 Feb 07 2017 14:30:04
%S 2,4,6,8,11,12,14,18,19,21,22,25,27,29,31,34,36,37,38,42,44,46,47,48,
%T 50,53,58,59,61,63,65,67,68,70,73,74,75,78,80,82,84,85,88,90,93,95,99,
%U 100,101,105,106,110,111,112,114,115,117,121,122,125,127,129,130,131,133
%N Numbers n such that the n-th prime is of the form 3k + 1/2 +- 1/2.
%C Numbers n such that the n-th prime is a generalized Cuban prime (A007645). A171820 UNION A091177 = A000027.
%C Essentially the same as A091178. - _R. J. Mathar_, Jan 28 2010
%e 2 is in the sequence because 2nd prime = 3*1 + 1/2 - 1/2;
%e 4 is in the sequence because 4th prime = 3*2 + 1/2 + 1/2.
%o (PARI) list(lim)=my(v=List(),n); forprime(p=2,, if(n++>lim, return(Vec(v))); if(p%3<2, listput(v,n))) \\ _Charles R Greathouse IV_, Feb 07 2017
%Y Cf. A000027, A000040, A007645, A091177.
%K nonn,less
%O 1,1
%A _Juri-Stepan Gerasimov_, Dec 19 2009