A117674 - OEIS

%I #17 Feb 08 2021 05:27:12

%S 3,19,37,73,109,127,163,181,271,307,433,523,541,613,631,811,1009,1063,

%T 1117,1153,1171,1423,1531,1621,1801,1999,2017,2053,2143,2161,2251,

%U 2341,2503,2521,3061,3313,3331,3511,3889,4051,4231,4789,4969,4987,5023,5113

%N Prime numbers whose sum of digits is a triangular number.

%H Amiram Eldar, <a href="/A117674/b117674.txt">Table of n, a(n) for n = 1..10000</a>

%e 1999 is in the sequence because it is a prime number and the sum of its digits 1+9+9+9 = 28 is a triangular number.

%t t={};Do[m = Total[IntegerDigits[Prime[n]]];If[IntegerQ[(Sqrt[8*m + 1]-1)/2],AppendTo[t, Prime[n]]],{n,700}];t  (* _Jayanta Basu_, Apr 27 2013 *)

%o (PARI) isok(p) = isprime(p) && ispolygonal(sumdigits(p), 3); \\ _Michel Marcus_, Feb 08 2021

%Y Intersection of A000040 and A187744.

%Y Cf. A000217, A007953.

%K nonn,base

%O 1,1

%A Luc Stevens (lms022(AT)yahoo.com), Apr 27 2006