A143421 Number of odd numbers k such that phi(k) = n, where n runs through the values (A002202) taken by phi.

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

Offset

1,4

Comments

The first zero term is for n = 16842752 = 257*2^16. If there are only five Fermat primes, then terms will be zero for n=2^r for all r>31. This is discussed in problem E3361.

a(2698482) = 0. That is, the 2698482nd term of A002202 is 16842752. - T. D. Noe, Aug 19 2008

References

R. K. Guy, Unsolved problems in number theory, B39.

Links

T. D. Noe, Table of n, a(n) for n=1..10000

T. D. Noe, Numbers Like 16842752

William P. Wardlaw, L. L. Foster and R. J. Simpson, Problem E3361, Amer. Math. Monthly, Vol. 98, No. 5 (May, 1991), 443-444.

Formula

A058277(n) = A143421(n) + A143422(n).

Crossrefs

Sequence in context: A025893 A296977 A025878 * A137672 A141272 A281527

Adjacent sequences: A143418 A143419 A143420 * A143422 A143423 A143424

Keyword

nonn

Author

T. D. Noe, Aug 14 2008

Status

approved