A081373 Number of values of k, 1 <= k <= n, with A000010(k) = A000010(n).

1, 2, 1, 2, 1, 3, 1, 2, 2, 3, 1, 4, 1, 3, 1, 2, 1, 4, 1, 3, 2, 2, 1, 4, 1, 3, 2, 4, 1, 5, 1, 2, 2, 3, 1, 5, 1, 3, 2, 4, 1, 6, 1, 3, 3, 2, 1, 5, 2, 4, 1, 4, 1, 4, 2, 5, 2, 2, 1, 6, 1, 2, 3, 2, 1, 5, 1, 3, 1, 6, 1, 7, 1, 4, 3, 5, 2, 8, 1, 4, 1, 4, 1, 9, 1, 3, 1, 5, 1, 10, 2, 2, 3, 2, 3, 5, 1, 4, 4, 6

Offset

1,2

Links

Paul Tek, Table of n, a(n) for n = 1..100000

Example

n=16: phi(k) = {1,1,2,2,4,2,6,4,6,4,10,4,12,6,8,8} for k=1,...,n; 2 numbers exist with phi(k) = phi(n) = 8: {15,16}, so a(16)=2.
If n=p is an odd prime number, then a(p)=1 with phi(k) = p-1.

Mathematica

f[x_] := Count[Table[EulerPhi[j]-EulerPhi[x], {j, 1, x}], 0] Table[f[w], {w, 1, 100}]

Prog

(PARI) a(n)=my(t=eulerphi(n), s); sum(k=1, n, eulerphi(n)==t) \\ Charles R Greathouse IV, Feb 21 2013

Crossrefs

Cf. A000010, A067004.

Sequence in context: A072527 A345138 A343945 * A029436 A263274 A333940

Adjacent sequences: A081370 A081371 A081372 * A081374 A081375 A081376

Keyword

nonn

Author

Labos Elemer, Mar 24 2003

Status

approved