cp's OEIS Frontend

A170820 Let p = n-th prime; a(n) = (p-1)/(order of (p+3)/2 mod p).

%I A170820 #13 Dec 03 2018 15:12:14
%S A170820 2,1,1,3,1,6,2,4,1,1,1,2,2,4,1,5,2,10,2,3,1,1,12,4,1,1,1,1,1,1,1,2,2,
%T A170820 1,1,2,2,2,1,5,2,2,4,3,42,1,1,1,1,2,8,1,1,2,4,1,1,7,2,4,6,2,2,4,30,2,
%U A170820 1,1,1,2,1,3,2,2,2,1,25,4,11,1,10,2,3,1,1,8,10,33,1,2,3,1,6,2,4,1,2,1,2,2,1
%N A170820 Let p = n-th prime; a(n) = (p-1)/(order of (p+3)/2 mod p).
%H A170820 Alois P. Heinz, <a href="/A170820/b170820.txt">Table of n, a(n) for n = 3..65536</a>
%H A170820 I. Anderson and D. A. Preece, <a href="http://dx.doi.org/10.1016/j.disc.2008.09.046">Combinatorially fruitful properties of 3*2^(-1) and 3*2^(-2) modulo p</a>, Discr. Math., 310 (2010), 312-324.
%p A170820 with(numtheory); [seq((ithprime(n)-1)/order((ithprime(n)+3)/2,ithprime(n)),n=3..130)];
%t A170820 a[n_] := Module[{p=Prime[n]}, (p-1)/MultiplicativeOrder[(p+3)/2, p]]; Array[a, 100, 3] (* _Amiram Eldar_, Dec 03 2018 *)
%o A170820 (PARI) a(n) = my(p=prime(n)); (p-1)/znorder(Mod((p+3)/2, p)); \\ _Michel Marcus_, Dec 03 2018
%Y A170820 Cf. A014664, A001917, A170821, A170822.
%K A170820 nonn
%O A170820 3,1
%A A170820 _N. J. A. Sloane_, Dec 24 2009