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

%I A163505 #16 Jun 27 2024 09:01:12
%S A163505 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,
%T A163505 58,58,58,60,62,62,66,66,66,66,70,70,72,72,74,76,76,78,78,82,82,82,82,
%U A163505 86,90,90,90,90,90,92,92,92,92,92,94,98,100,100,104,104,104,104,106,106
%N A163505 a(n) = (n-th odd nonprime) mod (n-th odd number).
%H A163505 G. C. Greubel, <a href="/A163505/b163505.txt">Table of n, a(n) for n = 1..1000</a>
%F A163505 a(n) = A014076(n) mod A005408(n-1). [corrected by _R. J. Mathar_, Oct 10 2009]
%e A163505 a(1) =  1 mod 1 = 0;
%e A163505 a(2) =  9 mod 3 = 0;
%e A163505 a(3) = 15 mod 5 = 0;
%e A163505 a(4) = 21 mod 7 = 0;
%e A163505 a(5) = 25 mod 9 = 7.
%p A163505 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:
%p A163505 A163505 := proc(n) A014076(n) mod (2*n-1); end: seq(A163505(n),n=1..80) ; # _R. J. Mathar_, Oct 10 2009
%t A163505 A014076 := Select[Range[1, 10000, 2], PrimeOmega[#] != 1 &]; Table[Mod[A014076[[n]], 2*n - 1], {n,1,50}] (* _G. C. Greubel_, Jul 27 2017 *)
%Y A163505 Cf. A005408, A014076.
%K A163505 nonn
%O A163505 1,5
%A A163505 _Juri-Stepan Gerasimov_, Jul 29 2009
%E A163505 Missing term between a(53) and a(54) inserted by _G. C. Greubel_, Jul 27 2017