A356485 a(n) = n! * Sum_{k=1..n} A000010(k)/k.
1, 3, 13, 64, 416, 2736, 23472, 207936, 2113344, 22584960, 284722560, 3576337920, 52240412160, 768727895040, 12228344755200, 206114911027200, 3838718125670400, 71231050830643200, 1468632692485324800, 30345814652977152000, 666456931810639872000, 15172961921551171584000
Offset: 1
Keywords
Links
- Eric Weisstein's World of Mathematics, Totient Function.
Programs
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Mathematica
Table[n! * Sum[EulerPhi[k]/k, {k, 1, n}], {n, 1, 25}] -
PARI
a(n) = n!*sum(k=1, n, eulerphi(k)/k); \\ Michel Marcus, Aug 09 2022
Formula
a(n) ~ n! * 6*n/Pi^2.