A309308 Least number k with A309004(k) = n.

1, 12, 60, 420, 4620, 360, 1021020, 19399380, 446185740, 13860, 401120980260, 2520, 608500527054420, 26165522663340060, 180180, 65178316954380089460, 3845520700308425278140, 234576762718813941966540, 15716643102160534111758180, 27720, 3063060, 6435289534681345815798169108260

Offset: 1

Author

Amiram Eldar, Jul 22 2019

Keywords

• nonn

Examples

			a(3) = 60 since 60 is the least number with 3 numbers having the same prime signature and set of distinct prime factor as 60: 60 = 2^2 * 3 * 5, 90 = 3^2 * 2 * 5, and 150 = 5^2 * 2 * 3.
		

Crossrefs

Cf. A088860, A111470, A309004.

Subsequence of A025487.

Programs

Mathematica

a[n_] := Multinomial @@ Tally[FactorInteger[n][[;;,2]]][[;;,2]]; m = 6; s = Table[0, {m}]; c = 0; n = 1; While[c < m, i = a[n]; If[i <= m && s[[i]] == 0, s[[i]] = n; c++]; n++]; s

Formula

a(k) <= A088860(k).