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 A227936 #14 May 10 2014 09:52:59 %S A227936 21,28,36,55,78,136,171,190,231,378,435,595,1035,1275,1378,2278,2415, %T A227936 2775,4095,5778,5995,7875,8778,10878,11175,11935,14535,14878,21115, %U A227936 26335,27495,31375,31878,36315,37675,42195,47895,52975,55278,60378,66795,68635,75078 %N A227936 Triangular numbers which become primes when their rightmost digit is removed. %H A227936 K. D. Bajpai, <a href="/A227936/b227936.txt">Table of n, a(n) for n = 1..10000</a> %e A227936 a(3)=36: T(8)=36. Removing the rightmost digit gives 3, which is prime. %e A227936 a(9)=231: T(21)=231. Removing the rightmost digit gives 23, which is prime. %p A227936 KD := proc(n) local a, b, d; a :=n/2*(n+1); b:=floor(a/10); if isprime(b) then return (a) end if; end proc: seq(KD(n), n=1..10); %Y A227936 Cf. A225873, A225885. %K A227936 nonn,base,less %O A227936 1,1 %A A227936 _K. D. Bajpai_, Oct 06 2013