This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A387201 #22 Sep 02 2025 23:39:00 %S A387201 1,4,8,9,32,36,48,74,112,186,204,364,393,572,781,1208,2624,2778,4522, %T A387201 4896,5272,32884 %N A387201 Numbers k such that 32 * 3^k + 1 is prime. %C A387201 a(23) > 10^5. %C A387201 Conjecture: This sequence intersects with A387197 at k = 4 to form twin primes with center N = 2^5 * 3^4 = 2592 = A027856(10). Any such intersection has to be at an even k because if k is odd, either N-1 or N+1 has to be divisible by 5. A covering system can be constructed that eliminates all other intersections except where k = 4(mod 60), and for k > 4 with k = 4(mod 60), the search up to 10^5 makes the probability of another intersection in this residue class vanishingly small. %H A387201 Ken Clements, <a href="/A387201/a387201_2.py.txt">Python program to calculate covering system.</a> %t A387201 Select[Range[0, 5000], PrimeQ[32 * 3^# + 1] &] (* _Amiram Eldar_, Aug 21 2025 *) %o A387201 (Python) %o A387201 from gmpy2 import is_prime %o A387201 print([ k for k in range(4000) if is_prime(32 * 3**k + 1)]) %Y A387201 Cf. A027856, A003306, A005537, A005538, A387060, A387197. %K A387201 nonn,more,new %O A387201 1,2 %A A387201 _Ken Clements_, Aug 21 2025