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 A217381 #22 Jul 24 2025 03:26:44 %S A217381 2,6,10,26,42,58,68,196,266,602,1170,1288,1290,2990,4110,6292,7446, %T A217381 36928,57490,65478,78570,188832,273452 %N A217381 Numbers k such that 8^k + 7 is prime. %C A217381 All terms are equal to 1/3 of the multiples of 3 in A057195. %C A217381 Naturally these numbers are even because (9-1)^(2n+1)+7 is divisible by 3. - _Bruno Berselli_, Oct 03 2012 %t A217381 Select[Range[10000], PrimeQ[8^# + 7] &] %o A217381 (PARI) is(n)=ispseudoprime(8^n+7) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A217381 Cf. A057195, A217354, A217355. %Y A217381 Cf. A144360 (associated primes). %K A217381 nonn,more %O A217381 1,1 %A A217381 _Vincenzo Librandi_, Oct 02 2012 %E A217381 a(18)-a(22) from A057195 by _Robert Price_, Jul 23 2017 %E A217381 a(23) from the data at A057195 added by _Amiram Eldar_, Jul 23 2025