A307015 Smallest number with same number of divisors as 3*a(n-1).

1, 2, 6, 12, 36, 60, 180, 360, 840, 2520, 7560, 15120, 45360, 55440, 166320, 498960, 720720, 2162160, 6486480, 10810800, 32432400, 61261200, 183783600, 551350800, 1102701600, 2327925600, 6983776800, 20951330400, 48886437600, 146659312800, 374796021600, 1124388064800

Offset

1,2

Comments

Question: is the intersection of this sequence and A019505 infinite?

Links

Table of n, a(n) for n=1..32.

Example

36*3=108 has 12 divisors; smallest number with 12 divisors is 60.

Mathematica

With[{s = DivisorSigma[0, Range[10^7]]}, Nest[Append[#, First@ FirstPosition[s, DivisorSigma[0, 3 Last@ #]]] &, {1}, 18]] (* Michael De Vlieger, Mar 21 2019 *)

Prog

(PARI) least(x) = {my(k=1, nd = numdiv(x)); while (numdiv(k) != nd, k++); k; }
lista(nn) = {my(a = 1); print1(a, ", "); for (n=2, nn, a = least(3*a); print1(a, ", "); ); } \\ Michel Marcus, Mar 20 2019

Crossrefs

Cf. A019505.

Sequence in context: A099576 A303479 A347452 * A026549 A120766 A121404

Adjacent sequences: A307012 A307013 A307014 * A307016 A307017 A307018

Keyword

nonn

Author

J. Lowell, Mar 19 2019

Extensions

a(17)-a(21) from Michel Marcus, Mar 20 2019

a(22)-a(32) from Giovanni Resta, Mar 22 2019

Status

approved