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

0,2

Links

Table of n, a(n) for n=0..9.

Example

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.

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 *)

Crossrefs

Cf. A000005, A033950.

Sequence in context: A289897 A134054 A323716 * A229865 A134086 A297566

Adjacent sequences: A360803 A360804 A360805 * A360807 A360808 A360809

Keyword

nonn,more

Author

Ctibor O. Zizka, Feb 21 2023

Extensions

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

Status

approved