A371966 Largest number reachable starting from 1 and taking n steps either doubling or doubling+reversing.

1, 2, 4, 8, 61, 221, 442, 884, 8671, 24371, 60721, 244121, 881371, 2898371, 8692591, 48826601, 97653202, 484336211, 968672422, 6847550561, 24334620331, 68473110671, 247696944631, 884738088671, 2892570042961, 8872433043671, 44817108207511, 89634216415022, 486415512459511

Offset

0,2

Comments

At each step you are allowed to either double x -> 2*x or double and reverse x -> R(2*x), where R(x) = A004086(x) is decimal digit reversal.

Links

Michael S. Branicky, Table of n, a(n) for n = 0..34

Formula

a(n) <= 20^n and a(n+1) <= 20*a(n).

Example

a(4) = 61 by the path 1, 2, 4, 8, 61.

Prog

(Python)
from itertools import islice
def reverse(n): return int(str(n)[::-1])
def agen(): # generator of terms
    reach = {1}
    while True:
        yield max(reach)
        newreach = set()
        for q in reach: newreach.update([2*q, reverse(2*q)])
        reach = newreach
print(list(islice(agen(), 28))) # Michael S. Branicky, Apr 14 2024

Crossrefs

Cf. A004086, A371880.

Sequence in context: A028910 A018482 A036447 * A263451 A339951 A069027

Adjacent sequences: A371963 A371964 A371965 * A371967 A371968 A371969

Keyword

nonn,base

Author

Bryle Morga and Michael S. Branicky, Apr 14 2024

Status

approved