[seqfan] (3^n+1)/2 is prime, A171381

N. J. A. Sloane njas at research.att.com
Sun Jun 13 07:24:58 CEST 2010

```Jon S. corrected this sequence.  After 9 incorrect terms

%I A171381
%S A171381 1,2,4,16,32,64
%N A171381 Numbers n such that (3^n + 1)/2 is prime.
%C A171381 Note that n must be a power of 2.
%C A171381 The next term, if it exists, is at least 2^15. - Jon Schoenfield, Jun 12 2010.
%e A171381 For n = 1 we obtain a(1) = (3^1 + 1)/2 = 2 which is a prime.
%Y A171381 Cf. A138083.
%Y A171381 Sequence in context: A173746 A095803 A032464 this_sequence A145119 A081411 A094384
%Y A171381 Adjacent sequences: A171378 A171379 A171380 this_sequence A171382 A171383 A171384
%K A171381 nonn,more,new
%O A171381 1,2
%A A171381 Joao Carlos Leandro da Silva (zxawyh66(AT)yahoo.com), Dec 07 2009
%E A171381 Edited by N. J. A. Sloane, Dec 09 2009
%E A171381 Incorrect terms a(7)-a(15) deleted Jun 12 2010 by Jon Schoenfield

(or in other words, 0,1,2,4,5,6,>=15)

Can anyone find the next term?  (Otherwise it is awfully close to the
powers of 2)

Neil

```