A245351 Sum of digits of n written in fractional base 10/7.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 21, 22, 23, 24, 25, 26, 27, 28

Offset: 0

Author

Hailey R. Olafson, Jul 18 2014

Keywords

• nonn
• base
• easy

Comments

The base 10/7 expansion is unique and thus the sum of digits function is well-defined.

Examples

			In base 10/7 the number 14 is represented by 74 and so a(14) = 7 + 4 = 11.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 0..10000
• Index entries for sequences related to fractional bases.

Crossrefs

Cf. A000120, A007953, A024662, A244040.

Programs

Mathematica

a[n_] := a[n] = If[n == 0, 0, a[7 * Floor[n/10]] + Mod[n, 10]]; Array[a, 100, 0] (* Amiram Eldar, Aug 04 2025 *)

PARI

a(n) = if(n == 0, 0, a(n\10 * 7) + n % 10); \\ Amiram Eldar, Aug 04 2025

Sage

# uses [basepqsum from A245355]
[basepqsum(10,7,w) for w in [0..200]]

Formula

a(n) = A007953(A024662(n)).