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A049305
Numbers k such that k is a substring of 7^k.
2
3, 4, 6, 8, 12, 15, 20, 40, 42, 43, 50, 53, 55, 59, 60, 61, 62, 69, 72, 73, 74, 75, 78, 79, 80, 81, 83, 86, 87, 88, 89, 93, 94, 95, 96, 97, 99, 100, 103, 111, 113, 114, 118, 164, 165, 185, 193, 200, 207, 210, 215, 220, 230, 232, 238, 241, 243, 250, 253, 254, 255
OFFSET
1,1
PROG
(Python)
def ok(n): return str(n) in str(7**n)
print(list(filter(ok, range(256)))) # Michael S. Branicky, Aug 13 2021
CROSSREFS
KEYWORD
nonn,base,easy
STATUS
approved