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

Author

Juri-Stepan Gerasimov, Jul 29 2009

Keywords

• nonn

Examples

			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.
		

Links

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

Crossrefs

Cf. A005408, A014076.

Programs

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 *)

Formula

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

Extensions

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