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A261388 a(n) is the length of the longest stretch of consecutive primitive roots of the multiplicative group modulo prime(n).

%I A261388 #13 Aug 18 2015 13:19:21
%S A261388 1,1,2,1,3,2,3,3,3,2,3,4,3,3,4,5,5,2,3,3,3,3,7,6,5,4,5,6,4,3,4,4,5,4,
%T A261388 6,4,4,4,6,5,6,3,5,4,5,3,4,5,7,4,7,6,4,5,6,7,9,4,4,4,9,5,4,5,4,6,4,3,
%U A261388 8,6,7,8,5,5,4,8,5,3,5,7,8,6,6,4,4,6,9,5,4,4,11,11,5,5,5,8,7,5,6
%N A261388 a(n) is the length of the longest stretch of consecutive primitive roots of the multiplicative group modulo prime(n).
%H A261388 Joerg Arndt, <a href="/A261388/b261388.txt">Table of n, a(n) for n = 1..9592</a> (terms for all primes < 10^5)
%t A261388 a[n_] := 1 + Max[ Join[{0}, Length/@ Select[ Split@ Differences @ PrimitiveRootList @ Prime @ n, #[[1]] == 1 &]]]; Array[a, 99] (* _Giovanni Resta_, Aug 17 2015 *)
%o A261388 (PARI)
%o A261388 consec_pr(p)= \\ max number of consecutive primroots
%o A261388 {
%o A261388     my( v = vector(p-1) );
%o A261388     my (g = znprimroot(p) );
%o A261388     for (j=1, p-1,  if (gcd(p-1,j)==1, v[lift(g^j)]=1 ) );
%o A261388     my ( m=0, t=0 );
%o A261388     for (j=1, p-1, if ( v[j]==0, t=0 , t+=1; if ( t>m, m=t ); ); );
%o A261388     return(m);
%o A261388 }
%o A261388 forprime(p=2,10^3, c=consec_pr(p);  print1( c,", " ); );
%Y A261388 Cf. A261438 (primes corresponding to records).
%K A261388 nonn
%O A261388 1,3
%A A261388 _Joerg Arndt_, Aug 17 2015