This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A064382 #6 Aug 04 2025 11:32:38 %S A064382 1,6,240,100800,605404800,65703372134400,155590841484029952000, %T A064382 9416463528385701835407360000,16689045681854870055279680279347200000, %U A064382 976264092939656812770160178186221444104192000000,2097176933095579995533106263090939623313258344938995712000000 %N 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. %F A064382 a(n) = 2^(n-1) * A022915(n) = 2^(n-1) * (n*(n+1)/2)!/(1!*2!*...*n!). %Y A064382 Cf. A022915. %K A064382 nonn %O A064382 1,2 %A A064382 Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Sep 27 2001 %E A064382 Corrected and extended by _Vladeta Jovovic_, Sep 28 2001