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 A147846 #12 Jun 13 2025 06:16:37
%S A147846 1,3,6,10,15,21,28,55,66,78,91,136,153,171,190,253,276,406,435,465,
%T A147846 496,666,703,820,861,903,946,1081,1128,1378,1431,1711,1770,1830,1891,
%U A147846 2211,2278,2485,2556,2628,2701,3081,3160,3403,3486,3916,4005,4656,4753,5050
%N A147846 Triangular numbers n*(n+1)/2 with n or n+1 prime.
%H A147846 Charles R Greathouse IV, <a href="/A147846/b147846.txt">Table of n, a(n) for n = 1..10000</a>
%F A147846 a(n) ~ (n^2 log^2 n)/8. - _Charles R Greathouse IV_, Jun 03 2013
%F A147846 A034953 UNION A008837. - _R. J. Mathar_, Jun 13 2025
%o A147846 (PARI) lista(nn) = {for (n=1, nn, if (isprime(n) || isprime(n+1), print1(n*(n+1)/2, ", ")););} \\ _Michel Marcus_, Jun 03 2013
%o A147846 (PARI) print1(1);forprime(p=3,7,print1(", "p*(p-1)/2", "p*(p+1)/2)) \\ _Charles R Greathouse IV_, Jun 03 2013
%Y A147846 Cf. A000217, A034953, A008837.
%K A147846 nonn,easy
%O A147846 1,2
%A A147846 _Giovanni Teofilatto_, Nov 15 2008
%E A147846 Missing terms 28=7*8/2, 91=13*14/2 etc. inserted by _R. J. Mathar_, Jan 30 2010