A068128 Triangular numbers with sum of digits = 6.

6, 15, 105, 231, 2211, 3003, 20301, 112101, 2003001, 122000010, 200030001, 20000300001, 2000003000001, 200000030000001, 20000000300000001, 2000000003000000001, 200000000030000000001, 20000000000300000000001, 2000000000003000000000001

Offset

1,1

Comments

1. The sequence is unbounded, as the (2*10^k +1)-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

Table of n, a(n) for n=1..19.

Mathematica

Select[Accumulate[Range[20000002]], Total[IntegerDigits[#]]==6&] (* Harvey P. Dale, Jun 05 2012 *)

Crossrefs

Intersection of A000217 and A052220.

Cf. A068127.

Sequence in context: A194265 A129521 A029765 * A013222 A013228 A133472

Adjacent sequences: A068125 A068126 A068127 * A068129 A068130 A068131

Keyword

base,easy,nonn

Author

Amarnath Murthy, Feb 21 2002

Extensions

More terms from Sascha Kurz, Mar 06 2002

More terms from Sean A. Irvine, Mar 17 2023

Offset changed by Andrew Howroyd, Sep 17 2024

Status

approved