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A320848
Number of 2-element subsets of [n] whose sum is a triangular number.
2
1, 1, 2, 3, 4, 5, 7, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 29, 32, 34, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 73, 77, 80, 83, 86, 89, 93, 97, 101, 105, 109, 112, 116, 120, 124, 128, 132, 136, 140, 145, 150, 154, 158, 162, 166, 170, 174, 179, 184, 189
OFFSET
2,3
LINKS
CROSSREFS
Column k=2 of A284249.
Cf. A000217.
Sequence in context: A077273 A032955 A375581 * A228234 A360792 A060526
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 22 2018
STATUS
approved