A098598 Number of primes in sequences formed from the t digits of n where the latter terms are given by rule b(i)=sum of t previous terms; primes are counted from initial t digits up to the largest term < n^2.
5, 5, 5, 5, 5, 5, 4, 3, 4, 2, 3, 7, 2, 6, 1, 6, 1, 5, 1, 4, 3, 6, 7, 2, 7, 5, 1, 5, 5, 1, 0, 6, 1, 5, 0, 6, 0, 7, 0, 5, 3, 6, 7, 6, 6, 2, 6, 7, 5, 6, 0, 5, 1, 1, 0, 6, 0, 5, 0, 0, 3, 5, 6, 5, 5, 5, 6, 2, 5, 5, 0, 3, 1, 4, 0, 4, 0, 5, 0, 4, 0, 4, 8, 1, 3, 4, 0, 6, 6, 0, 4, 4, 6, 3, 4, 3, 3, 3, 2, 4, 6, 7, 4, 7, 2
Offset: 10
Examples
a(21)=7 because there are 7 primes in the sequence 2,1,3,4,7,11,18,29,47,76,123,199,322.