A068131 Triangular numbers with sum of digits = 21.

1596, 2775, 3486, 3828, 4278, 4656, 5565, 6555, 7626, 8256, 9453, 14196, 15753, 16653, 17391, 18336, 21945, 22791, 23871, 24753, 28920, 32385, 34716, 37128, 38226, 39621, 40755, 42195, 43365, 44850, 46056, 51681, 54615, 56280, 57630

Offset: 1

Author

Amarnath Murthy, Feb 21 2002

Keywords

• base
• easy
• nonn

Comments

1. The sequence is unbounded, as the (5*10^k + 6)-th triangular number is a term. 2. The sum of the digits of triangular numbers in most cases is a triangular number. 3. Conjecture: For every triangular number T there exist infinitely many triangular numbers with sum of digits = T.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Subsequence of A000217.

Cf. A068127, A068128, A068129, A068130.

Programs

Mathematica

Select[Accumulate[Range[400]],Total[IntegerDigits[#]]==21&] (* Harvey P. Dale, Jun 06 2015 *)

Extensions

More terms from Sascha Kurz, Mar 06 2002

Offset changed by Andrew Howroyd, Sep 19 2024