%I A129755
%S A129755 1,3,21,91,153,171,231,253,561,741,1081,1653,1711,1891,2211,2701,3321,
               3403,
%T A129755 4851,6441,8001,9453,9591,10153,12403,15051,16471,17391,18721,23653,24753,
%U A129755 27261,30381,32131,35511,38781,39621,41041,44253,45753,51681,55611,56953
%N A129755 Triangular numbers t such that t+10 is a prime.
%C A129755 The only triangular numbers t such that t-10 is a prime are 15 and 21.
%p A129755 t1:=[]; f:=n->n*(n+1)/2; for n from 1 to 1000 do if isprime(f(n)+10) 
               then t1:=[op(t1),f(n)]; fi; od: t1; [from N. J. A. Sloane (njas(AT)research.att.com), 
               Jun 01 2007]
%t A129755 Select[Table[n(n+1)/2,{n,400}],PrimeQ[ #+10]&]
%o A129755 (PARI) for(k=1, 100, t=(k*(k+1))/2; if(isprime(t+10), print1(t, ", "))) 
               [from Joerg Arndt, Jun 01 2007]
%Y A129755 Sequence in context: A034490 A071351 A083231 this_sequence A059826 A108970 
               A069017
%Y A129755 Adjacent sequences: A129752 A129753 A129754 this_sequence A129756 A129757 
               A129758
%K A129755 nonn
%O A129755 1,2
%A A129755 Zak Seidov (zakseidov(AT)yahoo.com), May 15 2007
%E A129755 Checked by N. J. A. Sloane (njas(AT)research.att.com), Jun 01 2007