A377952 Numbers k that divide A084190(k) = lcm{d-1 : d > 1 and d|k}.

1, 30, 60, 90, 105, 132, 180, 210, 252, 264, 360, 380, 420, 495, 504, 520, 528, 546, 630, 660, 756, 840, 858, 870, 924, 990, 1040, 1056, 1092, 1140, 1224, 1260, 1320, 1365, 1485, 1512, 1530, 1560, 1638, 1656, 1716, 1722, 1740, 1785, 1820, 1848, 1900, 1980, 2040

Offset: 1

Author

Amiram Eldar, Nov 12 2024

Keywords

• nonn
• easy

Comments

After the first term a(1) = 1, the next odd term is a(5) = 105, the next term that is coprime to 6 is a(133) = 6545, and the next term that is coprime to 30 is a(322) = 19019.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A084190.

A377953 is a subsequence.

Similar sequences: A056954, A355331, A377950.

Programs

Mathematica

Select[Range[2000], # == 1 || Divisible[LCM @@ (Rest @ Divisors[#] - 1), #] &]

PARI

is(k) = !(lcm(apply(x -> if(x > 1, x-1, x), divisors(k))) % k);