A101778 Last term in each row of triangle referenced in A101777.

3, 5, 3, 2, 7, 5, 3, 7, 7, 5, 3, 2, 11, 7, 7, 5, 3, 13, 11, 7, 7, 5, 3, 2, 13, 13, 11, 7, 7, 5, 3, 17, 13, 13, 11, 7, 7, 5, 3, 2, 19, 17, 13, 13, 11, 7, 7, 5, 3, 19, 19, 17, 13, 13, 11, 7, 7, 5, 3, 2, 23, 19, 19, 17, 13, 13, 11, 7, 7, 5, 3, 23, 23, 19, 19, 17, 13, 13, 11, 7, 7, 5, 3, 2, 23

Offset: 1

Author

Ray Chandler, Jan 10 2005

Keywords

• nonn

Links

• Jinyuan Wang, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A100555, A101776, A101777.

Programs

PARI

A020482(k) = forprime(q=2, k, if(isprime(2*k-q), return(2*k-q)));
a(n) = {my(r=(ceil(sqrt(2*n+1)))^2-2*n+3); if(r%2==0, r=A020482(r/2), if(isprime(r-2), r-=2, r=A020482(r\2))); r; } \\ Jinyuan Wang, Jan 29 2020

Formula

a(n) = A101777(A000217(n)).