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A011872 [ n(n-1)/19 ]. 0
0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 4, 5, 6, 8, 9, 11, 12, 14, 16, 18, 20, 22, 24, 26, 29, 31, 34, 36, 39, 42, 45, 48, 52, 55, 59, 62, 66, 70, 74, 78, 82, 86, 90, 95, 99, 104, 108, 113, 118, 123, 128, 134, 139, 145, 150, 156, 162, 168, 174, 180, 186, 192, 199, 205, 212, 218, 225, 232 (list; graph; refs; listen; history; internal format)
OFFSET

0,8

FORMULA

a(n) = +2*a(n-1) -a(n-2) +a(n-19) -2*a(n-20) +a(n-21). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 15 2010]

CROSSREFS

Sequence in context: A034139 A060620 A109968 * A056822 A062419 A061052

Adjacent sequences:  A011869 A011870 A011871 * A011873 A011874 A011875

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com).

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Last modified February 15 21:56 EST 2012. Contains 205860 sequences.