A171253 - OEIS

%I #8 Jan 02 2023 12:30:47

%S 5,17,19,65,67,79,4097,4099,4111,4159,65537,65539,65551,65599,69631,

%T 262145,262147,262159,262207,266239,327679,1073741825,1073741827,

%U 1073741839,1073741887,1073745919,1073807359,1074003967

%N Semi-sums (average) of any two distinct Mersenne primes (A000668).

%C Subsequence of A171252, excluding the terms of A000668 itself.

%H Jonathan Vos Post, <a href="http://list.seqfan.eu/oldermail/seqfan/2010-March/003808.html">Sums of three Mersenne primes, and prime sums of three Mersenne primes</a>, SeqFan list, Mar 5, 2010.

%F a(n) = A171252(A014132(n)).

%F A171253 = A171252 \ A000688.

%e a(1) = (A000668(2)+A000668(1))/2, a(2) = (A000668(3)+A000668(1))/2, a(3) = (A000668(3)+A000668(2))/2, a(4) = (A000668(4)+A000668(1))/2, ,...

%o (PARI) concat(vector(#A000668,i,vector(i-1,j,A000668[i]+A000668[j])))/2 /* having defined A000668 as vector with initial terms of A000668 */

%Y Cf. A171252 (includes terms of A000668), A171255 (primes in this sequence).

%K nonn

%O 1,1

%A _M. F. Hasler_, Mar 06 2010