This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A129540 #10 Jan 23 2025 10:23:57 %S A129540 1711,1891,4851,9591,18721,23653,24753,27261,32131,35511,57291,64261, %T A129540 69751,77421,79401,81003,102831,106491,108811,114003,115921,147153, %U A129540 153181,155403,171991,178503,181503,191271,200661,208981,219453 %N A129540 Triangular numbers T such that T+10 is the next prime after T. %p A129540 a := proc (n) if nextprime((1/2)*n*(n+1)) = 10+(1/2)*n*(n+1) then (1/2)*n*(n+1) else end if end proc: seq(a(n), n = 1 .. 700); # _Emeric Deutsch_, Jun 20 2007 %t A129540 Select[Accumulate[Range[0, 700]],NextPrime[#]==#+10&] (* _James C. McMahon_, Jan 22 2025 *) %Y A129540 Cf. A000217, A129755. %K A129540 nonn %O A129540 1,1 %A A129540 _Zak Seidov_, May 29 2007 %E A129540 More terms from _Emeric Deutsch_, Jun 20 2007