A066969 Numbers k such that Sum_{i=1..k} phi(i)/gcd(k,i) is an integer.

1, 4, 9, 16, 27, 36, 63, 64, 108, 112, 121, 132, 192, 256, 375, 432, 464, 625, 768, 961, 1024, 1296, 1309, 1600, 1620, 2205, 2304, 2525, 2597, 3072, 3136, 3888, 4096, 4913, 6561, 8100, 8500, 8993, 10064, 10816, 12352, 13689, 15376, 16384, 20480, 25600, 26000, 28672

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..100

Formula

If k = 4^j, j >= 0, k is in the sequence.

Mathematica

Select[Range[1000], IntegerQ[Sum[EulerPhi[i]/GCD[#, i], {i, 1, #}]] &] (* Amiram Eldar, Jun 06 2022 *)

Prog

(PARI) isok(n) = type(sum(i=1, n, eulerphi(i)/gcd(n, i))) == "t_INT"; \\ Michel Marcus, Nov 20 2013

Crossrefs

Cf. A066970.

Sequence in context: A180306 A138994 A195618 * A213495 A109593 A237589

Adjacent sequences: A066966 A066967 A066968 * A066970 A066971 A066972

Keyword

nonn

Author

Benoit Cloitre, Jan 26 2002

Extensions

More terms from Michel Marcus, Nov 20 2013

Status

approved