A101778 - OEIS

%I #6 Jan 29 2020 02:51:50

%S 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,

%T 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,

%U 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

%N Last term in each row of triangle referenced in A101777.

%H Jinyuan Wang, <a href="/A101778/b101778.txt">Table of n, a(n) for n = 1..10000</a>

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

%o (PARI) A020482(k) = forprime(q=2, k, if(isprime(2*k-q), return(2*k-q)));

%o 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

%Y Cf. A100555, A101776, A101777.

%K nonn

%O 1,1

%A _Ray Chandler_, Jan 10 2005