OFFSET
1,4
COMMENTS
The least k, if it exists, such that prime(n) divides 10^k + 1.
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = A068958(n) for n > 3. - Georg Fischer, Oct 23 2018
MATHEMATICA
Table[p = Prime[n]; s = Select[Range[p/2], PowerMod[10, #, p] == p - 1 &, 1]; If[s == {}, 0, s[[1]]], {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Apr 14 2014
STATUS
approved