A330648 a(1) = 1 and for any n > 1, if A330647(n) divides a(n-1) then a(n) = a(n-1) / A330647(n), otherwise a(n) = a(n-1) * A330647(n).

1, 2, 6, 30, 5, 20, 140, 1260, 126, 1386, 18018, 1287, 10296, 858, 14586, 277134, 12597, 201552, 4635696, 193154, 2897310, 111435, 3120180, 156009, 7429, 133722, 3343050, 96948450, 3231615, 100180065, 3205762080, 94287120, 3488623440, 91805880, 2295147

Offset

1,2

Comments

This sequence has similarities with A008336.

Links

Rémy Sigrist, Table of n, a(n) for n = 1..1000

Example

The first terms, alongside the corresponding A330647(n), are:
  n   a(n)  A330647(n)
  --  ----  ----------
   1     1           1
   2     2           2
   3     6           3
   4    30           5
   5     5           6
   6    20           4
   7   140           7
   8  1260           9
   9   126          10
  10  1386          11

Mathematica

Nest[Append[#1, Block[{k = 2, s}, While[Nand[FreeQ[#1[[All, 1]], k], MemberQ[{1, k}, Set[s, GCD[#3, k]]]], k++]; {k, If[s == 1, #3 k, #3/k], If[Mod[#3, k] == 0, #3/k, #3 k]}]] & @@ {#, #[[-1, 1]], #[[-1, 2]], #[[-1, -1]]} &, {{1, 1, 1}}, 34][[All, -1]] (* Michael De Vlieger, Dec 23 2019 *)

Prog

(PARI) x=1; s=0; for (n=1, 35, for (v=1, oo, if (!bittest(s, v), if (gcd(x, v)==1, s+=2^v; x*=v; break, x%v==0, s+=2^v; x/=v; break))); print1 (x", "))

Crossrefs

Cf. A008336, A330647.

Sequence in context: A326900 A373350 A181812 * A354418 A074168 A079615

Adjacent sequences: A330645 A330646 A330647 * A330649 A330650 A330651

Keyword

nonn

Author

Rémy Sigrist, Dec 22 2019

Status

approved