A105935 Indices of Lucas 7-step numbers A104621 which have a nontrivial divisor in common with index.
6, 12, 18, 20, 21, 33, 36, 42, 54, 57, 60, 65, 87, 93, 99, 100, 104, 105, 108, 111, 141, 147, 152, 153, 155, 156, 162, 165, 171, 177, 180, 189, 192, 195, 210, 215, 220, 222, 230, 235, 238, 240, 249, 255, 261, 264, 273, 276, 279, 280, 286, 294, 295, 297, 300
Offset: 1
Examples
gcd(a(n), A104621(6,12,18,33,36,57,60,87,93,108)) = 3, gcd(a(n), A104621(20,65,100,105)) = 5, gcd(a(n), A104621(21,42)) = 7, gcd(a(n), A104621(54,99)) = 9, gcd(a(n), A104621(104)) = 13.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
m=300; s = LinearRecurrence[{1, 1, 1, 1, 1, 1, 1}, {7, 1, 3, 7, 15, 31, 63}, m+1]; Select[Range[m], !CoprimeQ[#, s[[#+1]]] &] (* Amiram Eldar, Sep 05 2019 *)
Formula
gcd(a(n), A104621(a(n))) > 1.
Extensions
Offset corrected and a(5)-a(6) and more terms added by Amiram Eldar, Sep 05 2019
Comments