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A051304 Number of 4-element proper antichains of an n-element set. 1
0, 0, 0, 0, 5, 780, 41545, 1442910, 39400305, 923889960, 19550316665, 384954289170, 7196416532305, 129495073447740, 2264887575116985, 38775513868485030 (list; graph; refs; listen; history; internal format)
OFFSET

0,5

FORMULA

(1/4!) * (16^n -18*12^n +60*10^n -9*9^n -102*8^n +105*7^n -90*6^n +95*5^n -31*4^n -33*3^n +28*2^n -6)

CROSSREFS

Cf. A032263, A036239, A051112.

Sequence in context: A171269 A172890 A195612 * A060713 A198402 A085706

Adjacent sequences:  A051301 A051302 A051303 * A051305 A051306 A051307

KEYWORD

nonn

AUTHOR

Vladeta Jovovic, Goran Kilibarda, Zoran Maksimovic (vladeta(AT)eunet.rs)

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Last modified February 15 12:25 EST 2012. Contains 205786 sequences.