A227936 - OEIS

%I #14 May 10 2014 09:52:59

%S 21,28,36,55,78,136,171,190,231,378,435,595,1035,1275,1378,2278,2415,

%T 2775,4095,5778,5995,7875,8778,10878,11175,11935,14535,14878,21115,

%U 26335,27495,31375,31878,36315,37675,42195,47895,52975,55278,60378,66795,68635,75078

%N Triangular numbers which become primes when their rightmost digit is removed.

%H K. D. Bajpai, <a href="/A227936/b227936.txt">Table of n, a(n) for n = 1..10000</a>

%e a(3)=36: T(8)=36. Removing the rightmost digit gives 3, which is prime.

%e a(9)=231: T(21)=231. Removing the rightmost digit gives 23, which is prime.

%p 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 Cf. A225873, A225885.

%K nonn,base,less

%O 1,1

%A _K. D. Bajpai_, Oct 06 2013