OFFSET
1,1
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
MATHEMATICA
Select[Accumulate[Range[400]], Total[IntegerDigits[#]]==21&] (* Harvey P. Dale, Jun 06 2015 *)
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Feb 21 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 06 2002
Offset changed by Andrew Howroyd, Sep 19 2024
STATUS
approved