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 A265482 #19 Aug 22 2025 17:35:45 %S A265482 1,2,5,9,19,25,54,104,112,120,177,317,504,540,734,780,1649,1923,2715, %T A265482 4308,5917,6494,7305,22653,26888,71448,93834,137027,158472,174648 %N A265482 Numbers k such that 16^k - 4^k - 1 is prime. %C A265482 For k = 1, 2, 5, 9, 19, 25, the corresponding primes are 11, 239, 1047551, 68719214591, 75557863725639445512191, 1267650600228228275596796362751. %C A265482 a(n) is not of the form 5*k+6 (divisibility by 11) or 9*k+8 (divisibility by 19) or 7*k+3*(-1)^k (divisibility by 29). %C A265482 Conjecture: the odd terms are not of the form 8*k+7. %C A265482 k is in the sequence iff 2*k is in A098845 (terms a(21)-a(30) are derived from that sequence). - _Ray Chandler_, Sep 25 2019 %e A265482 5 is in the sequence because 16^5-4^5-1 = 1047551 is prime. %t A265482 Select[Range[2500], PrimeQ[16^# - 4^# - 1] &] %o A265482 (Magma) [n: n in [0..500] | IsPrime(16^n-4^n-1)]; %o A265482 (PARI) is(n)=ispseudoprime(16^n-4^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A265482 Cf. A098845, similar sequences listed in A265481. %K A265482 nonn,more %O A265482 1,2 %A A265482 _Vincenzo Librandi_, Dec 10 2015