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 A341639 a(1) = 1; a(n+1) = Sum_{d|n} phi(d) * a(d) * a(n/d). 0
 1, 1, 2, 6, 19, 95, 291, 2037, 10203, 71429, 357240, 3929640, 19648533, 255430929, 1788018540, 16092167088, 144829514049, 2462101738833, 17234712244012, 327459532636228, 2947135794083881, 38312765323095109, 421440418557975839, 9693129626833444297, 87238166641520673597 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS FORMULA a(1) = 1; a(n+1) = Sum_{k=1..n} a(gcd(n,k)) * a(n/gcd(n,k)). MATHEMATICA a[1] = 1; a[n_] := a[n] = Sum[EulerPhi[d] a[d] a[(n - 1)/d], {d, Divisors[n - 1]}]; Table[a[n], {n, 25}] a[1] = 1; a[n_] := a[n] = Sum[a[GCD[n - 1, k]] a[(n - 1)/GCD[n - 1, k]], {k, n - 1}]; Table[a[n], {n, 25}] CROSSREFS Cf. A000010, A038044, A038045, A332791. Sequence in context: A266933 A291106 A079453 * A186770 A332406 A127942 Adjacent sequences:  A341636 A341637 A341638 * A341640 A341641 A341642 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Feb 16 2021 STATUS approved

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Last modified January 18 05:57 EST 2022. Contains 350436 sequences. (Running on oeis4.)