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 A271361 #11 May 02 2024 22:54:59 %S A271361 1,2,12,21,27,30,33,44,46,76,78,83,84,92,582,750,787,3218,3290,5617, %T A271361 6385,13960,22705,27636,36497,50349,51169,70381,70486,73096 %N A271361 Numbers k such that 63*10^k + 1 is prime. %C A271361 Numbers k such that the digits 63 followed by k-1 occurrences of the digit 0 followed by the digit 1 is prime (see Example section). %C A271361 a(31) > 10^5. %H A271361 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 630w1</a>. %e A271361 2 is in this sequence because 63*10^2+1 = 6301 is prime. %e A271361 Initial terms and associated primes: %e A271361 a(1) = 1, 631; %e A271361 a(2) = 2, 6301; %e A271361 a(3) = 12, 63000000000001; %e A271361 a(4) = 21, 63000000000000000000001; %e A271361 a(5) = 27, 63000000000000000000000000001, etc. %t A271361 Select[Range[0, 100000], PrimeQ[63*10^#+1] &] %o A271361 (PARI) is(n)=ispseudoprime(63*10^n+1) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A271361 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A271361 nonn,more %O A271361 1,2 %A A271361 _Robert Price_, Apr 05 2016