A227936 Triangular numbers which become primes when their rightmost digit is removed.

21, 28, 36, 55, 78, 136, 171, 190, 231, 378, 435, 595, 1035, 1275, 1378, 2278, 2415, 2775, 4095, 5778, 5995, 7875, 8778, 10878, 11175, 11935, 14535, 14878, 21115, 26335, 27495, 31375, 31878, 36315, 37675, 42195, 47895, 52975, 55278, 60378, 66795, 68635, 75078

Offset: 1

Author

K. D. Bajpai, Oct 06 2013

Keywords

• nonn
• base
• less

Examples

			a(3)=36: T(8)=36. Removing the rightmost digit gives 3, which is prime.
a(9)=231: T(21)=231. Removing the rightmost digit gives 23, which is prime.
		

Links

• K. D. Bajpai, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A225873, A225885.

Programs

Maple

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);