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A064366 Special binomial coefficient: a(n) = C(sigma(n), phi(n)). 3
1, 3, 6, 21, 15, 66, 28, 1365, 1716, 3060, 66, 20475, 91, 134596, 735471, 7888725, 153, 3262623, 190, 118030185, 225792840, 254186856, 276, 2558620845, 84672315, 11058116888, 113380261800, 558383307300, 435, 11969016345, 496 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..200

FORMULA

a(n) = C(A000203(n), A000010(n)); at prime indices it gives triangular numbers (A034953(p)).

MATHEMATICA

Array[Binomial[DivisorSigma[1, #], EulerPhi@ #] &, 31] (* Michael De Vlieger, Nov 03 2017 *)

PROG

(PARI) { for (n=1, 200, write("b064366.txt", n, " ", binomial(sigma(n), eulerphi(n))) ) } \\ Harry J. Smith, Sep 12 2009

CROSSREFS

Cf. A000203, A000010, A034953, A066090, A066449.

Sequence in context: A019051 A019042 A019052 * A260157 A101719 A173165

Adjacent sequences:  A064363 A064364 A064365 * A064367 A064368 A064369

KEYWORD

nonn

AUTHOR

Labos Elemer, Sep 27 2001

STATUS

approved

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Last modified March 26 22:42 EDT 2019. Contains 321565 sequences. (Running on oeis4.)