A163505 a(n) = (n-th odd nonprime) mod (n-th odd number).

0, 0, 0, 0, 7, 5, 7, 5, 5, 7, 7, 5, 5, 3, 5, 3, 3, 5, 3, 3, 3, 1, 1, 46, 46, 48, 52, 1, 1, 58, 58, 58, 58, 58, 60, 62, 62, 66, 66, 66, 66, 70, 70, 72, 72, 74, 76, 76, 78, 78, 82, 82, 82, 82, 86, 90, 90, 90, 90, 90, 92, 92, 92, 92, 92, 94, 98, 100, 100, 104, 104, 104, 104, 106, 106

Offset

1,5

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Formula

a(n) = A014076(n) mod A005408(n-1). [corrected by R. J. Mathar, Oct 10 2009]

Example

a(1) =  1 mod 1 = 0;
a(2) =  9 mod 3 = 0;
a(3) = 15 mod 5 = 0;
a(4) = 21 mod 7 = 0;
a(5) = 25 mod 9 = 7.

Maple

A014076 := proc(n) option remember; local a; if n = 1 then 1; else for a from procname(n-1)+2 by 2 do if not isprime(a) then return a; end if; end do: end if; end proc:
A163505 := proc(n) A014076(n) mod (2*n-1); end: seq(A163505(n), n=1..80) ; # R. J. Mathar, Oct 10 2009

Mathematica

A014076 := Select[Range[1, 10000, 2], PrimeOmega[#] != 1 &]; Table[Mod[A014076[[n]], 2*n - 1], {n, 1, 50}] (* G. C. Greubel, Jul 27 2017 *)

Crossrefs

Cf. A005408, A014076.

Sequence in context: A021573 A080411 A178988 * A021136 A214444 A194657

Adjacent sequences: A163502 A163503 A163504 * A163506 A163507 A163508

Keyword

nonn

Author

Juri-Stepan Gerasimov, Jul 29 2009

Extensions

Missing term between a(53) and a(54) inserted by G. C. Greubel, Jul 27 2017

Status

approved