A038457 |First digit-last digit| for triangular numbers.

0, 0, 0, 0, 1, 4, 1, 6, 3, 1, 0, 0, 1, 8, 4, 1, 5, 2, 0, 1, 2, 1, 1, 4, 3, 2, 2, 5, 2, 1, 1, 2, 3, 4, 0, 6, 0, 4, 6, 7, 8, 7, 6, 3, 9, 4, 0, 7, 5, 4, 4, 5, 7, 0, 4, 1, 5, 2, 0, 1, 1, 0, 2, 4, 2, 3, 1, 6, 4, 3, 3, 4, 6, 1, 3, 2, 4, 0, 2, 3, 3, 2, 0, 3, 3, 2, 2, 5, 3, 1, 1, 2, 4, 3, 1, 4, 2, 1, 3, 4, 5

Offset: 0

Author

Felice Russo

Keywords

• easy
• nonn
• base

Crossrefs

Cf. A000217.

Programs

Mathematica

Abs[IntegerDigits[#][[1]]-IntegerDigits[#][[-1]]]&/@Accumulate[ Range[ 0,120]] (* Harvey P. Dale, Mar 22 2020 *)

Formula

a(n) = A040163(A000217(n)). - Michel Marcus, Sep 27 2013