A007960 -id:A007960 - cp's OEIS frontend

A187744 Numbers whose digital sum is a triangular number.

0, 1, 3, 6, 10, 12, 15, 19, 21, 24, 28, 30, 33, 37, 42, 46, 51, 55, 60, 64, 69, 73, 78, 82, 87, 91, 96, 100, 102, 105, 109, 111, 114, 118, 120, 123, 127, 132, 136, 141, 145, 150, 154, 159, 163, 168, 172, 177, 181, 186, 190, 195, 201, 204, 208, 210, 213, 217

Offset: 1

Dario Piazzalunga, Jan 03 2013

Every term with some permutations can become another term of this sequence.
The subsequence of primes begins: 3, 19, 37, 73, 91, 127...
The subsequence of triangular numbers begins: 1, 3, 6, 10, 15, 21, 28, 55...

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A000217, A007960, A000027.

a187744 n = a187744_list !! (n-1)
a187744_list = filter ((== 1) . a010054 . a007953) [0..]
-- Reinhard Zumkeller, Jan 03 2013

TriangularQ[n_] := IntegerQ[Sqrt[1 + 8 n]]; Select[Range[0, 300], TriangularQ[Total[IntegerDigits[#]]] &] (* T. D. Noe, Jan 03 2013 *)

If decimal expansion of n is x1 x2 ... xk then x1 + x2 + ... xk = T.

A010054(A007953(a(n))) = 1. - Reinhard Zumkeller, Jan 03 2013

cp's OEIS Frontend

A187744 Numbers whose digital sum is a triangular number.

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