A359964 Refactorable numbers (A033950) having more divisors than all smaller refactorable numbers.

1, 2, 8, 12, 24, 36, 60, 180, 240, 360, 720, 1260, 1680, 3360, 5040, 10080, 15120, 20160, 25200, 30240, 55440, 100800, 110880, 221760, 277200, 443520, 665280, 720720, 1108800, 1441440, 2494800, 2882880, 3603600, 5765760, 8648640, 12972960, 14414400, 25945920, 28828800

Offset

1,2

Comments

The corresponding numbers of divisors are 1, 2, 4, 6, 8, 9, 12, 18, 20, 24, ... .

This sequence if infinite since there are refactorable numbers with arbitrarily large number of divisors. E.g., for any prime p, p^(p-1) is a refactorable number with p divisors.

Links

Amiram Eldar, Table of n, a(n) for n = 1..60

Mathematica

seq[nmax_] := Module[{s = {}, dm = 0, d}, Do[d = DivisorSigma[0, n]; If[d > dm && Divisible[n, d], dm = d; AppendTo[s, n]], {n, 1, nmax}]; s]; seq[10^6]

Prog

(PARI) lista(nmax) = {my(dm = 0, d); for(n = 1, nmax, d = numdiv(n); if(d > dm && n%d == 0, dm = d; print1(n, ", "))); }

Crossrefs

Subsequence of A033950.

Cf. A000005, A073904, A110821.

Similar sequences: A002182, A335317, A356078, A359963.

Sequence in context: A162152 A280252 A013654 * A277804 A108978 A269968

Adjacent sequences: A359961 A359962 A359963 * A359965 A359966 A359967

Keyword

nonn

Author

Amiram Eldar, Jan 20 2023

Status

approved