A242831 - OEIS

%I #15 May 25 2014 00:12:59

%S 10,21,136,153,351,630,780,3403,3570,5671,6441,6670,7503,9870,10011,

%T 13366,14535,16653,20301,23220,33153,34716,36046,36315,37950,43660,

%U 46360,56616,66430,93096,93961,95703,112101,139656,144453,159895,166753,169653,187578

%N Triangular numbers T such that sum of the factorials of digits of T is prime.

%C The n-th triangular number T(n) = n * (n+1)/2.

%C Intersection of A165451 and A000217.

%H K. D. Bajpai, <a href="/A242831/b242831.txt">Table of n, a(n) for n = 1..10000</a>

%e 16*(16+1)/2 = 136 is triangular number. 1! + 3! + 6! = 727 which is prime. Hence 136 appears in the sequence.

%e 35*(35+1)/2 = 630 is triangular number. 6! + 3! + 0! = 727 which is prime. Hence 630 appears in the sequence.

%p A242831:= proc()  if isprime(add( i!,i = convert((x*(x+1)/2), base, 10))(x*(x+1)/2))then RETURN ((x*(x+1)/2)); fi; end: seq(A242831 (), x=1..1000);

%Y Cf. A000040, A000217, A061602, A165451.

%K nonn,base

%O 1,1

%A _K. D. Bajpai_, May 23 2014