A091381 - OEIS

%I #3 Dec 08 2015 23:59:30

%S 0,2,1,5,2,3,3,1,9,1,7,3,3,1,9,6,2,6,-1,4,8,5,5,6,7,1,5,2,3,14,5,5,3,

%T 10,1,7,6,1,9,6,2,5,4,7,1,13,11,5,2,3,2,2,15,5,4,9,1,7,3,3,10,14,-5,8,

%U 7,14,3,13,2,3,2,12,7,6,1,9,8,3,4,15,2,5,4,8,5,5,6,7,1,5,1,18,5,8,1,9,11,3,18

%N First differences of A091380.

%C Seemingly, the difference sequence is mostly positive. There are special characteristic features, where it is nonpositive (see A091383-A091385).

%H Ferenc Adorjan, <a href="http://web.axelero.hu/fadorjan/qrp.pdf">The sequence of largest quadratic residues modulo the primes</a>

%o (PARI) {/* Difference sequence of the largest "mixed" QR modulo the primes */ d_lqxr(to)=local(v=[],k,r,q,p,e=1); for(i=2,to,p=prime(i);k=p-1;r=p%4-2; while(kronecker(k,p)<>r,k-=1); v=concat(v,k-e);e=k); print(v) }

%Y Cf. A091380, A091382, A091383, A091384, A091385, A088191, A088197.

%K easy,sign

%O 1,2

%A Ferenc Adorjan (fadorjan(AT)freemail.hu)