A066090 -id:A066090 - cp's OEIS frontend

A066449 Binomial(n, phi(n)), where phi(n) is the Euler totient function.

1, 2, 3, 6, 5, 15, 7, 70, 84, 210, 11, 495, 13, 3003, 6435, 12870, 17, 18564, 19, 125970, 293930, 646646, 23, 735471, 53130, 9657700, 4686825, 30421755, 29, 5852925, 31, 601080390, 573166440, 2203961430, 417225900, 1251677700, 37, 33578000610

Offset: 1

Joseph L. Pe, Dec 28 2001

This is also binomial(n, cototient(n)). - Franklin T. Adams-Watters, Jul 13 2014

			a(6) = binomial(6, phi(6)) = binomial(6, 2) = 6!/(2!*4!) = 15.

Harry J. Smith, Table of n, a(n) for n=1..300

Cf. A000010, A051953, A066090, A064366.

seq(binomial(n, numtheory:-phi(n)), n=1..100); # Robert Israel, Jul 13 2014

Map[Binomial[#, EulerPhi[#]] &, Range[80]] (* Carl Najafi, Aug 30 2011 *)

{ for (n=1, 300, a=binomial(n, eulerphi(n)); write("b066449.txt", n, " ", a) ) } \\ Harry J. Smith, Feb 15 2010

a(16) - a(38) from Harry J. Smith, Feb 15 2010

A064366 a(n) = binomial(sigma(n), phi(n)).

Original entry on oeis.org

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, 366395202809685, 16735679449896, 21094923659355

Offset: 1

Labos Elemer, Sep 27 2001

nonn

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

Cf. A000010, A000203, A000217, A034953, A066090, A066449.

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

a(n) = { binomial(sigma(n), eulerphi(n)) } \\ Harry J. Smith, Sep 12 2009

a(n) = binomial(A000203(n), A000010(n));

a(p) = A000217(p) for prime p.

cp's OEIS Frontend

A066449 Binomial(n, phi(n)), where phi(n) is the Euler totient function.

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