A393200 - OEIS

A393200

a(n) is the least value of m such that the sum of the digits of n in base m is coprime with n.

2, 2, 2, 2, 6, 2, 2, 2, 8, 2, 8, 2, 2, 2, 2, 2, 12, 2, 12, 5, 2, 2, 14, 2, 2, 2, 2, 2, 18, 2, 2, 2, 6, 2, 6, 2, 2, 2, 12, 2, 24, 2, 2, 2, 4, 2, 26, 2, 2, 2, 2, 2, 30, 3, 2, 2, 4, 2, 8, 2, 2, 6, 2, 2, 36, 2, 8, 3, 2, 2, 14, 2, 2, 2, 2, 2, 42, 2, 8, 3, 2, 2, 44, 2, 4, 2, 2, 2

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OFFSET

2,1

COMMENTS

It is well-defined, the expression of every n >= 2 in base n is 10, and the sum of its digits, 1+0=1, is always coprime with n.

LINKS

Sean A. Irvine, Table of n, a(n) for n = 2..1000

MATHEMATICA

Table[First@Select[Range[2, n], CoprimeQ[n, Total[IntegerDigits[n, #], 1]] &], {n, 2, 100}]

PROG

(PARI) a(n) = my(m=2); while (gcd(sumdigits(n, m), n) != 1, m++); m; \\ Michel Marcus, Feb 07 2026

CROSSREFS