A305739 a(n) = n!*T(n) - 1, where T(n) is the n-th triangular number.
0, 5, 35, 239, 1799, 15119, 141119, 1451519, 16329599, 199583999, 2634508799, 37362124799, 566658892799, 9153720575999, 156920924159999, 2845499424767999, 54420176498687999, 1094805903679487999, 23112569077678079999, 510909421717094399999
Offset: 1
Keywords
Crossrefs
Programs
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Maple
seq(n*(n+1)!/2-1,n=1..21);
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PARI
a(n) = n*(n+1)!/2 - 1; \\ Michel Marcus, Jun 23 2018
Formula
a(n) = n*(n+1)!/2 - 1. - Michel Marcus, Jun 23 2018