The number of palindromic primes leading and ending with 1, 3, 7 or 9 -- in sequence -- of length 2*ceiling(n/4)+1.

A220248

The number of palindromic primes leading and ending with 1, 3, 7 or 9 -- in sequence -- of length 2*ceiling(n/4)+1.

Terms

    a(0) =5a(1) =4a(2) =4a(3) =2a(4) =25a(5) =27a(6) =24a(7) =18a(8) =190a(9) =172a(10) =155a(11) =151a(12) =1424a(13) =1280a(14) =1243a(15) =1225a(16) =10924a(17) =10512a(18) =10399a(19) =10207a(20) =92015a(21) =88693a(22) =87149a(23) =85844a(24) =788498a(25) =767916a(26) =744036a(27) =736193a(28) =6891972a(29) =6755263

External references