A355457 Numbers k > 1 such that A354833(k) = k * A354833(k-1).

2, 3, 4, 7, 15, 26, 31, 43, 98, 117, 140, 215, 540, 1945, 22279, 38459, 39461, 66869, 69328, 4047994, 4615259, 5617480, 5898979, 9685120, 9751023

Offset: 1

Author

Rémy Sigrist, Jul 02 2022

Keywords

• nonn
• more

Comments

This sequence gives indexes of multiplicative steps in A354833.

Examples

			For k = 7:
- A354833(7) = 91 = 7 * 13 = 7 * A354833(6),
- so 7 is a term.
		

Crossrefs

Cf. A354833.

Programs

PARI

{ seen = Map(); v = 1; for (n=2, oo, mapput(seen, v, 0); v=if (mapisdefined(seen, w=v-n) || w<0, print1 (n", "); v*n, w)) }

Python

from itertools import count, islice
def agen():
    an, seen = 1, {1}
    for n in count(2):
        t = an - n
        if t not in seen and t >= 0: an = t
        else: an *= n; yield n
        seen.add(an)
print(list(islice(agen(), 25))) # Michael S. Branicky, Jul 02 2022

Extensions

a(20)-a(25) from Michael S. Branicky, Jul 02 2022