A380798 a(n) is the smallest prime p such that tau(p^2 - 1) is equal to 2^n, where tau = A000005.

2, 3, 5, 11, 29, 109, 379, 1429, 4159, 23869, 188189, 2147419, 13470731, 71469971, 573015871, 4272944831, 23731864001

Offset

1,1

Links

Table of n, a(n) for n=1..17.

Mathematica

a[n_]:=Module[{k=2}, While[DivisorSigma[0, k^2-1]!=2^n, k=NextPrime[k]]; k]; Array[a, 12] (* Stefano Spezia, Feb 04 2025 *)

Prog

(PARI) a(n) = my(p=2); while (numdiv(p^2-1) != 2^n, p=nextprime(p+1)); p; \\ Michel Marcus, Feb 04 2025

Crossrefs

Cf. A000005, A350780, A358881.

Sequence in context: A173631 A182987 A334814 * A364802 A360815 A087580

Adjacent sequences: A380795 A380796 A380797 * A380799 A380800 A380801

Keyword

nonn,more

Author

Juri-Stepan Gerasimov, Feb 03 2025

Extensions

a(14)-a(17) from Stefano Spezia, Feb 09 2025

Status

approved