# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a081318 Showing 1-1 of 1 %I A081318 #20 Apr 26 2022 18:45:06 %S A081318 6,18,22,30,32,38,42,46,54,66,74,78,82,90,94,96,110,118,132,138,146, %T A081318 154,162,174,186,194,198,206,210,218,228,231,240,242,254,258,260,264, %U A081318 266,268,274,282,284,286,298,300,306,310,318,322,334,338,344,348 %N A081318 Integers n such that the reciprocal of the largest prime factor of 10^n-1 is not a repeating decimal fraction with a period of n. %C A081318 For all but three of the terms through a(41)=274, the reciprocal of the largest prime factor of 10^a(n)-1 is a decimal fraction with a period of a(n)/2. Of the three exceptions, there are two (a(32)=231 and a(38)=264) where the period is a(n)/3, and one (a(19)=132) where the period is a(n)/4. - _Jon E. Schoenfield_, Jun 27 2010 %H A081318 Makoto Kamada, Factorizations of 11...11 (repunit). %F A081318 Integers n such that A061075(n) is not equal to A005422(n). %e A081318 30 is in the sequence because the factorization of 10^30-1 is 3^3*7*11*13*31*37*41*211*241*271*2161*9091*2906161 and 2906161 occurs already in 10^15-1=3^3*31*37*41*271*2906161 producing a decimal fraction with a period of 15, (1/2906161=0.000000344096559000000344096559000000344...) %Y A081318 Cf. A081317. %K A081318 more,nonn %O A081318 1,1 %A A081318 _Hugo Pfoertner_, Mar 18 2003 %E A081318 More terms from _Hans Havermann_, May 31 2003 %E A081318 Terms a(31)-a(37) from _Jon E. Schoenfield_, Jun 19 2010 %E A081318 Terms a(38)-a(41) added, link added, and earlier comment expanded by _Jon E. Schoenfield_, Jun 27 2010 %E A081318 a(42)-a(54) from _Max Alekseyev_, Aug 17 2013, Apr 26 2022 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE