A370858 - OEIS

A370858

Let L_1 = (1) and L_2 = (1, 2); for any n > 2, L_n is obtained by inserting one n between each pair of consecutive terms of L_{n-1} coprime to n; a(n) gives the number of terms in L_n.

1, 2, 3, 4, 7, 8, 15, 24, 43, 56, 111, 132, 263, 420, 723, 1040, 2079, 2472, 4943, 7448, 13091, 19236, 38471, 45884, 86119, 138024, 248459, 359142, 718283, 764160, 1528319, 2605756, 4858899, 7109964, 13809075, 16009784, 32019567, 52524888, 95697787, 125396930

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..40.

Rémy Sigrist, PARI program

FORMULA

a(p) = 2*a(p-1) - 1 for any odd prime number p.

EXAMPLE

The first terms, alongside the corresponding lists, are:

n a(n) L n

- ---- ---------------------------------------------

1 1 (1 )

2 2 (1, 2)

3 3 (1, 3, 2)

4 4 (1, 4, 3, 2)

5 7 (1, 5, 4, 5, 3, 5, 2)

6 8 (1, 6, 5, 4, 5, 3, 5, 2)

7 15 (1, 7, 6, 7, 5, 7, 4, 7, 5, 7, 3, 7, 5, 7, 2)

PROG

(PARI) See Links section.

CROSSREFS

Cf. A370857 (first differences).

Sequence in context: A120611 A092063 A227007 * A126850 A007497 A126882

Adjacent sequences: A370855 A370856 A370857 * A370859 A370860 A370861

KEYWORD

nonn

AUTHOR

Rémy Sigrist, Mar 03 2024

STATUS

approved