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A357430 a(n) is the least integer > 1 such that its digit representation in base n is equal to the digit representation in base n of the initial terms of its set of divisors in increasing order. 1
6, 48, 6, 182, 8, 66, 10, 102, 12, 1586, 14, 198, 16, 258, 18, 345, 20, 402, 22, 486, 24, 306484, 26, 678, 28, 786, 30, 26102, 32, 1026, 34, 1158, 36, 1335, 38, 1446, 40, 1602, 42, 204741669824, 44, 1938, 46, 2118, 48, 2355, 50, 2502, 52, 2706, 54, 8199524, 56 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,1
LINKS
FORMULA
a(2*n) = 2*n + 2 for any n > 1. - Rémy Sigrist, Sep 29 2022
PROG
(PARI) isok(k, b) = my(s=[]); fordiv(k, d, s=concat(s, digits(d, b)); if (fromdigits(s, b)==k, return(1)); if (fromdigits(s, b)> k, return(0)));
a(n) = my(k=2); while(! isok(k, n), k++); k;
(Python)
from sympy import divisors
from sympy.ntheory import digits
from itertools import count, islice
def ok(n, b):
target, s = digits(n, b)[1:], []
if target[0] != 1: return False
for d in divisors(n):
s += digits(d, b)[1:]
if len(s) >= len(target): return s == target
elif not target[:len(s)] == s: return False
def a(n):
return next(i for d in count(1) for i in range(n**d, 2*n**d) if ok(i, n))
print([a(n) for n in range(2, 41)]) # Michael S. Branicky, Oct 05 2022
CROSSREFS
Cf. A175252 (base 10), A357428 (base 2), A357429 (base 3).
Sequence in context: A321190 A320403 A354067 * A323138 A000252 A078237
KEYWORD
nonn,base
AUTHOR
Michel Marcus, Sep 28 2022
EXTENSIONS
More terms from Rémy Sigrist, Sep 29 2022
STATUS
approved

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Last modified May 27 21:25 EDT 2024. Contains 372882 sequences. (Running on oeis4.)