A064382 Number of ways to put numbers 1, 2, ..., n*(n+1)/2 in a triangular array of n rows in such a way that each row is increasing or decreasing.

1, 6, 240, 100800, 605404800, 65703372134400, 155590841484029952000, 9416463528385701835407360000, 16689045681854870055279680279347200000, 976264092939656812770160178186221444104192000000, 2097176933095579995533106263090939623313258344938995712000000

Offset: 1

Author

Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Sep 27 2001

Keywords

• nonn

Crossrefs

Cf. A022915.

Formula

a(n) = 2^(n-1) * A022915(n) = 2^(n-1) * (n*(n+1)/2)!/(1!*2!*...*n!).

Extensions

Corrected and extended by Vladeta Jovovic, Sep 28 2001