A384018 a(n) = [x^n] Product_{k=0..n-1} (1 + k*x)^3.
1, 0, 3, 63, 1767, 63690, 2822740, 148810032, 9104502015, 634448680884, 49622704133175, 4305280182748875, 410376649359397380, 42633179822414174760, 4794685285831034253660, 580373328155358031572600, 75234419898396217903091151, 10398952352945773993329785448, 1526704288048697734221906020641
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(i=0, n, sum(j=0, 2*n-i, abs(stirling(n, i, 1)*stirling(n, j, 1)*stirling(n, 2*n-i-j, 1))));
Formula
a(n) = Sum_{0<=i, j, k<=n and i+j+k=2*n} |Stirling1(n,i) * Stirling1(n,j) * Stirling1(n,k)|.