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A270033 a(n) is the smallest b for which the base-b representation of n contains at least one 7 (or 0 if no such base exists). 11
0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 8, 9, 10, 11, 12, 13, 14, 15, 8, 17, 9, 19, 10, 21, 11, 23, 8, 25, 13, 9, 14, 29, 10, 31, 8, 11, 17, 35, 9, 37, 19, 13, 8, 41, 14, 43, 11, 9, 23, 47, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 8, 10, 10, 10, 10, 10, 10, 10, 8, 11, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,7
COMMENTS
a(n) > 0 for n >= 15 since 17 is n written in base n-7.
The only perfect k-th powers (k >= 2) that can appear in this sequence are m^k with 2 <= m <= 7 and k a prime number.
LINKS
MATHEMATICA
Table[SelectFirst[Range[8, 1200], DigitCount[n, #, 7] > 0 &], {n, 15, 120}] (* Michael De Vlieger, Mar 10 2016, Version 10 *)
PROG
(PARI) a(n) = if ((n<15) && (n!=7), 0, my(b=8); while(!vecsearch(Set(digits(n, b)), 7), b++); b); \\ Michel Marcus, Mar 10 2016
CROSSREFS
Sequence in context: A180225 A353294 A127886 * A085121 A228634 A229659
KEYWORD
nonn,base
AUTHOR
Nathan Fox, Mar 08 2016
STATUS
approved

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Last modified March 4 22:06 EST 2024. Contains 370532 sequences. (Running on oeis4.)