A119905 Numbers k such that gcd(k, R_k) = 1, where R_k is the repunit (10^k -1)/9 = A002275(k).
1, 2, 4, 5, 7, 8, 10, 11, 13, 14, 16, 17, 19, 20, 23, 25, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43, 46, 47, 49, 50, 52, 53, 55, 56, 58, 59, 61, 62, 64, 65, 67, 68, 70, 71, 73, 74, 76, 77, 79, 80, 82, 83, 85, 86, 89, 91, 92, 94, 95, 97, 98, 100, 101, 103, 104, 106, 107
Offset: 1
Links
- T. D. Noe, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Select[Range[1000], GCD[#, (10^# - 1)/9] == 1&] (* Jean-François Alcover, May 19 2016 *)
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PARI
upto(N) = [n|n<-[1..N], 1==gcd(n, (10^n-1)/9)]; \\ Ruud H.G. van Tol, May 09 2024