A302387 a(n) is least number k >= 3 such that (k^(2^n) + (k-2)^(2^n))/2 is prime.
3, 3, 3, 5, 3, 3, 3, 179, 169, 935, 663, 8723, 1481, 2035, 10199, 18203, 36395
Offset: 0
Examples
a(10)=663 corresponds to the prime (663^1024 + 661^1024)/2.
Links
- Henri Lifchitz & Renaud Lifchitz, (36395^65536+36393^65536)/2, a(16).
Programs
-
Mathematica
lst = {}; For[n=0, n<=14, n++, k=3; While[! PrimeQ[(k^(2^n) + (k-2)^(2^n))/2], k++]; AppendTo[lst, k]]; lst (* Robert Price, Apr 29 2018 *) -
PARI
for(n=0,20,forstep(k=3,+oo,2,if(ispseudoprime((k^(2^n)+(k-2)^(2^n))/2),print1(k,", ");break())))
Extensions
a(15) from Robert Price, May 28 2018
a(16) from Kellen Shenton, Apr 14 2022