1,1

One less than count of members of n-th maximal chain of primes. For definitions see A152658.

Klaus Brockhaus, Table of n, a(n) for n=1..1000

The consecutive primes 5, 7, 11 form the first maximal chain of primes (see example in A152658); it has three members, two links. Therefore a(1) = 2.

(PARI) {n=1; while(n<560, c=0; while(isprime(n*prime(n)+(n+1)*prime(n+1)), c++; n++); if(c>0, print1(c, ", ")); n++)}

Cf. A152658 (beginnings of maximal chains of primes), A152657 (secluded primes), A119487 (primes of the form i*(i-th prime) + (i+1)*((i+1)-th prime), linking primes).

Sequence in context: A111879 A114732 A123338 this_sequence A046226 A054722 A067627

Adjacent sequences: A152732 A152733 A152734 this_sequence A152736 A152737 A152738

nonn

Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Dec 16 2008