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 A121773 Number of n-bead necklaces with n+1 colors for n>0, with a(0)=1. 2
 1, 2, 6, 24, 165, 1560, 19684, 299600, 5381685, 111111340, 2593758618, 67546215528, 1941507500933, 61054982558024, 2085209014017960, 76861433640597376, 3041324492665174641, 128583032925805678368, 5784852794346334629910, 275941052631578947368440 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Stefano Spezia, Table of n, a(n) for n = 0..350 FORMULA a(n) = (1/n)*Sum_{d|n} phi(n/d)*(n+1)^d, for n>0, with a(0)=1. a(n) is divisible by (n+1); a(n)/(n+1) = A121774(n). MATHEMATICA a[0] = 1; a[n_] := DivisorSum[n, (n+1)^# * EulerPhi[n/#] &] / n; Array[a, 20, 0] (* Amiram Eldar, Aug 15 2023 *) PROG (PARI) a(n)=if(n==0, 1, (1/n)*sumdiv(n, d, eulerphi(n/d)*(n+1)^d)) CROSSREFS Cf. A121774, A056665. Sequence in context: A038205 A012361 A308111 * A304996 A012711 A356579 Adjacent sequences: A121770 A121771 A121772 * A121774 A121775 A121776 KEYWORD nonn AUTHOR Paul D. Hanna, Aug 20 2006 EXTENSIONS a(18)-a(19) from Amiram Eldar, Aug 15 2023 STATUS approved

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Last modified July 15 14:37 EDT 2024. Contains 374332 sequences. (Running on oeis4.)