A360806 a(0) = 1; for n >= 1, a(n) is the least integer k > a(n-1) such that k / A000005(k) = a(n-1).

1, 2, 8, 80, 2240, 215040, 77414400, 61931520000, 170930995200000, 1340099002368000000

Offset: 0

Author

Ctibor O. Zizka, Feb 21 2023

Keywords

• nonn
• more

Examples

			a(0) = 1.
a(1) = 2 because the least k > 1 such that k / A000005(k) = 1 is k = 2.
a(2) = 8 because the least k > 2 such that k / A000005(k) = 2 is k = 8.
a(3) = 80 because the least k > 8 such that k / A000005(k) = 8 is k = 80.
and so on.
		

Crossrefs

Cf. A000005, A033950.

Programs

Mathematica

a[0] = 1; a[n_] := a[n] = Module[{m = a[n - 1], k}, k = 2*m; While[k != m*DivisorSigma[0, k], k += m]; k]; Array[a, 9, 0] (* Amiram Eldar, Feb 21 2023 *)

Extensions

a(5)-a(9) from Amiram Eldar, Feb 21 2023