A389296 Smallest k for which A386476(k) = n.

1, 4, 8, 16, 32, 64, 112, 144, 216, 288, 640, 432, 800, 1152, 864, 1296, 2808, 1728, 5200, 2592, 3456, 4320, 7344, 5184, 6048, 9072, 8640, 10368, 16848, 10800, 15120, 19008, 18144, 25200, 24192, 25920, 21600, 30240, 37800, 32400, 45360, 50400, 57024, 66528

Offset

1,2

Links

Table of n, a(n) for n=1..44.

Mathematica

s[n_] := DivisorSum[n, 1 &, And @@ CoprimeQ[# + {-1, 1}, n] &]; With[{max = 10^5}, v = Array[s, max]; TakeWhile[FirstPosition[v, #] & /@ Range[Max[v]] // Flatten, ! MissingQ[#] &]] (* Amiram Eldar, Sep 29 2025 *)

Prog

(Magma) [Min([k: k in [1..10^4] | #[d: d in Divisors(k) | Gcd(d^2 - 1, k) eq 1] eq n]): n in [1..24]];

Crossrefs

Cf. A386476.

Sequence in context: A145108 A108569 A342868 * A196875 A111073 A298807

Adjacent sequences: A389293 A389294 A389295 * A389297 A389298 A389299

Keyword

nonn

Author

Juri-Stepan Gerasimov, Sep 28 2025

Status

approved