A064440 Numbers k such that A048138(k) is a prime and sets a new record for such primes.

6, 21, 31, 79, 121, 265, 271, 379, 541, 631, 1051, 1351, 1597, 1711, 2071, 2401, 2551, 2761, 2881, 2941, 3811, 4111, 4471, 4531, 4621, 5251, 6091, 8341, 8371, 8401, 8821, 9871, 11551, 13651, 16171, 19531, 21211, 22681, 23101, 27931, 30661, 32551, 33811, 37591

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..188

Mathematica

seq[max_] := Module[{s = Table[0, {n, 1, max}], i, v = {}, m = 0}, Do[If[(i = DivisorSigma[1, n] - n) <= max, s[[i]]++], {n, 2, (max - 1)^2}]; Do[If[s[[i]] > m && PrimeQ[s[[i]]], m = s[[i]]; AppendTo[v, i]], {i, 1, max}]; v]; seq[2000] (* Amiram Eldar, Sep 23 2022 *)

Prog

(PARI) f(n) = my(s=0); for(x=1, n^2, if(sigma(x)-x==n, s++)); s;
a=0; for(n=1, 10^5, x=f(n); if(isprime(x), b=x; if(b>a, a=b; print1(n, ", "))))

Crossrefs

Cf. A001065, A048138, A238895, A238896.

Sequence in context: A239920 A173622 A302868 * A106634 A261077 A063126

Adjacent sequences: A064437 A064438 A064439 * A064441 A064442 A064443

Keyword

nonn

Author

Jason Earls, Oct 01 2001

Extensions

Corrected and extended by Matthew Conroy, Oct 02 2001

a(11)-a(44) from Amiram Eldar, Oct 01 2019

Status

approved