A334942 a(1) = 1, a(n) = a(n-1) / gcd(a(n-1),n) if this gcd is > 1, else a(n) = 2*a(n-1) + 4.

1, 6, 2, 1, 6, 1, 6, 3, 1, 6, 16, 4, 12, 6, 2, 1, 6, 1, 6, 3, 1, 6, 16, 2, 8, 4, 12, 3, 10, 1, 6, 3, 1, 6, 16, 4, 12, 6, 2, 1, 6, 1, 6, 3, 1, 6, 16, 1, 6, 3, 1, 6, 16, 8, 20, 5, 14, 7, 18, 3, 10, 5, 14, 7, 18, 3, 10, 5, 14, 1, 6, 1, 6, 3, 1, 6, 16, 8, 20, 1, 6

Offset

1,2

Comments

A variant of A133058.

Links

Table of n, a(n) for n=1..81.

Example

a(2) = 2*a(1) + 4 = 6, a(3) = a(2)/3 = 2, a(4) = a(3)/2 = 1, a(5) = 2*a(4) + 4 = 6, ...

Mathematica

a[1] = 1; a[n_] := a[n] = If[(g = GCD[a[n-1], n]) > 1, a[n-1]/g, 2*a[n-1] + 4]; Array[a, 100].

Prog

(PARI) lista(nn) = {my(va = vector(nn)); va[1] = 1; for (n=2, nn, my(g = gcd(va[n-1], n)); if (g > 1, va[n] = va[n-1]/g, va[n] = 2*va[n-1] + 4); ); va; } \\ Michel Marcus, May 17 2020

Crossrefs

Cf. A133058.

Sequence in context: A375741 A363684 A265986 * A217909 A334943 A002247

Adjacent sequences: A334939 A334940 A334941 * A334943 A334944 A334945

Keyword

nonn

Author

Ctibor O. Zizka, May 17 2020

Status

approved