A227936 - OEIS

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

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OFFSET

1,1

LINKS

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

EXAMPLE

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.

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);

CROSSREFS

Cf. A225873, A225885.