A128858 Number of digits in A128857(n).

1, 18, 28, 6, 42, 58, 22, 13, 44, 2, 108, 48, 21, 46, 148, 13, 78, 178, 6, 99, 18, 8, 228, 7, 41, 6, 268, 15, 272, 66, 34, 28, 138, 112, 116, 179, 5, 378, 388, 18, 204, 418, 6, 219, 32, 48, 66, 239, 81, 498, 508, 43, 506, 42, 60, 42, 284, 192, 90, 299, 84, 618, 48, 35

Offset: 1

Author

Anton V. Chupin (chupin(X)icmm.ru), Apr 12 2007

Keywords

• nonn
• base

Links

• A. V. Chupin, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A128857.

Programs

Mathematica

Give[a_,n_]:=Block[{d=Floor[Log[10,n]]+1,m=(10n-1)/GCD[10n-1,a]}, If[m?1,While[PowerMod[10,d,m]!=N,d++ ],d=1]; ((10^(d+1)-1) a n)/(10n-1)]; Length[IntegerDigits[Give[1,n]]]

Python

from sympy import n_order
def A128858(n): return n_order(10,10*n-1) # Chai Wah Wu, Apr 09 2024

Formula

a(n) = order of 10 (mod 10*n - 1). - Arkadiusz Wesolowski, Nov 17 2012

Extensions

a(10) = 2 corrected by Gerard P. Michon, Oct 31 2012