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

%I #7 Jul 03 2022 09:14:58

%S 2,3,4,7,15,26,31,43,98,117,140,215,540,1945,22279,38459,39461,66869,

%T 69328,4047994,4615259,5617480,5898979,9685120,9751023

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

%C This sequence gives indexes of multiplicative steps in A354833.

%e For k = 7:

%e - A354833(7) = 91 = 7 * 13 = 7 * A354833(6),

%e - so 7 is a term.

%o (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)) }

%o (Python)

%o from itertools import count, islice

%o def agen():

%o an, seen = 1, {1}

%o for n in count(2):

%o t = an - n

%o if t not in seen and t >= 0: an = t

%o else: an *= n; yield n

%o seen.add(an)

%o print(list(islice(agen(), 25))) # _Michael S. Branicky_, Jul 02 2022

%Y Cf. A354833.

%K nonn,more

%O 1,1

%A _Rémy Sigrist_, Jul 02 2022

%E a(20)-a(25) from _Michael S. Branicky_, Jul 02 2022