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A371966
Largest number reachable starting from 1 and taking n steps either doubling or doubling+reversing.
2
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
Sequence in context: A028910 A018482 A036447 * A263451 A339951 A069027
KEYWORD
nonn,base
AUTHOR
STATUS
approved