A341813 a(n) is the least integer k such that n/(Sum_{j=1..n} 1/phi(k*j)) is an integer.

1, 1, 4, 7, 2, 11, 22, 101, 53, 2, 25, 149, 75, 321, 10, 653, 3110, 907, 5926, 16829, 2505, 3174, 13178, 4323, 5931, 18033, 20231, 41698, 155533, 1323199, 1477613, 1133209, 65051, 109522, 152567, 610799, 33521, 8141, 2386, 156863, 239559, 1006091, 113097, 6353, 11434

Offset

1,3

Links

Table of n, a(n) for n=1..45.

Wikipedia, Harmonic mean.

Formula

a(n) <= A341810(n).

Prog

(PARI) a(n) = my(k=1); while (denominator(n/sum(j=1, n, 1/eulerphi(k*j))) != 1, k++); k; \\ Michel Marcus, Feb 20 2021

Crossrefs

Cf. A000010, A341810.

Sequence in context: A103887 A167046 A283745 * A088446 A362253 A076414

Adjacent sequences: A341810 A341811 A341812 * A341814 A341815 A341816

Keyword

nonn

Author

Seiichi Manyama, Feb 20 2021

Status

approved