A187126 - OEIS

A187126

Triangular numbers k*(k+1)/2 mod 1000, sorted and uniqued.

0, 1, 3, 5, 6, 10, 11, 15, 16, 20, 21, 25, 26, 28, 30, 31, 35, 36, 40, 41, 45, 46, 50, 51, 55, 56, 60, 61, 65, 66, 70, 71, 75, 76, 78, 80, 81, 85, 86, 90, 91, 95, 96, 100, 101, 105, 106, 110, 111, 115, 116, 120, 121, 125, 126, 128, 130, 131, 135, 136, 140

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

COMMENTS

Possible last three digits of triangular numbers k*(k+1)/2 (leading zeros omitted).

All triangular numbers less than 1000 belong to this sequence. The sequence is finite with 424 terms: a(424)=996 is the last term.

LINKS

Shyam Sunder Gupta, Table of n, a(n) for n = 1..424

EXAMPLE

The last three digits of k*(k+1)/2 can be 000, 001, 003, 021, 140, etc., but not 002, 004, 012, 139 etc.

MATHEMATICA

Union[Table[Mod[n*(n + 1)/2, 1000], {n, 1, 1000}]]