A105289 Indices of Lucas 5-step numbers A074048 which have a nontrivial divisor in common with index.

6, 12, 18, 20, 21, 33, 36, 48, 51, 54, 55, 60, 75, 78, 87, 99, 100, 108, 110, 112, 114, 120, 129, 132, 133, 144, 147, 153, 154, 155, 159, 162, 165, 174, 177, 180, 182, 183, 185, 195, 210, 219, 225, 228, 230, 234, 237, 245, 261, 267, 270, 275, 285, 290, 297, 310

Offset

1,1

Comments

Extension by T. D. Noe. Wanted: closed-form formula for this as exists for Fibonacci and Lucas numbers. See also A105764 (indices of prime Lucas 5-step numbers).

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

gcd(a(n), A074048(a(n))) > 1.

Example

gcd(6, A074048(6)) = gcd(6,57) = 3,
gcd(20, A074048(20)) = gcd(20,743775) = 5.
gcd(21, A074048(21)) = gcd(21,1462223) = 7.

Mathematica

m=300; s = LinearRecurrence[{1, 1, 1, 1, 1}, {5, 1, 3, 7, 15}, m+1]; Select[Range[m], !CoprimeQ[#, s[[#+1]]] &] (* Amiram Eldar, Sep 05 2019 *)

Crossrefs

Cf. A074048, A104714, A105764.

Sequence in context: A343126 A049094 A105935 * A328608 A328671 A051774

Adjacent sequences: A105286 A105287 A105288 * A105290 A105291 A105292

Keyword

easy,nonn

Author

Jonathan Vos Post, Apr 25 2005

Extensions

More terms from Amiram Eldar, Sep 05 2019

Status

approved