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 A084196 Number of primes q

%I

%S 0,0,1,1,3,0,2,1,5,2,2,0,3,1,6,3,6,0,1,7,0,3,6,4,1,2,2,6,0,3,3,5,2,3,

%T 3,3,0,1,9,2,9,1,8,0,3,3,1,4,6,0,3,11,0,8,2,8,6,3,0,2,1,5,3,7,0,2,1,0,

%U 5,1,2,13,2,0,3,10,3,0,2,0,11,0,11,2,5,5,6,0,4,2,6,13,2,5,2,13,4,4,1,0,1,4

%N Number of primes q<prime(n) such that q+1 divides prime(n)+1.

%C a(A049084(A082539(n)))=0, a(A049084(A084197(n)))>0, a(A049084(A084198(n)))=1;

%H Reinhard Zumkeller, <a href="/A084196/b084196.txt">Table of n, a(n) for n = 1..10000</a>

%e n=5, prime(5)=11: (11+1) mod (q+1) = 0 for 3 primes q<11: 2, 3,

%e and 5, therefore a(5)=3.

%o a084196 n = a084196_list !! (n-1)

%o a084196_list = f [] a000040_list where

%o f ps' (p:ps) = length [q | q <- ps', mod (p + 1) (q + 1) == 0] :

%o f (p : ps') ps where

%o -- _Reinhard Zumkeller_, Jan 06 2014

%Y Cf. A084198, A084200.

%K nonn

%O 1,5

%A _Reinhard Zumkeller_, May 18 2003

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Last modified November 27 03:56 EST 2021. Contains 349345 sequences. (Running on oeis4.)