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 A120819 #36 Aug 18 2025 05:50:03
%S A120819 171,277,367,561,567,18881
%N A120819 Indices of primes in A057137.
%C A120819 Digits are in ascending order beginning with 1 and after 9 comes 0.
%C A120819 Indices of primes in A057137.
%C A120819 All terms must end in 1 or 7: A057137(n) is even when n is even, and divisible by 3 iff n == 0, 2, 3, 5, 6, 8 or 9 (mod 10). - _M. F. Hasler_, Apr 14 2024
%C A120819 a(7) >= 100000. - _Michael S. Branicky_, Apr 07 2025
%D A120819 Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 61, 298.
%e A120819 a(1) = 12345678901234567890...01234567890...012345678901 = A057137(171) is the first prime term in A057137.
%t A120819 fQ[n_] := PrimeQ@ FromDigits@ Mod[Range@n, 10]; lst = {}; Do[ If[fQ@n, AppendTo[lst, n]; Print@n], {n, 10000}]; lst
%t A120819 IntegerLength[Select[Table[FromDigits[PadRight[{},n,{1,2,3,4,5,6,7,8,9,0}]],{n,1,1001,2}],PrimeQ]] (* _Harvey P. Dale_, Feb 07 2024 *)
%o A120819 (PARI) N=0;for(n=1,600,if(ispseudoprime(N=10*N+n%10),print1(n", "))) \\ _Charles R Greathouse IV_, May 10 2014 (Comment: Surprisingly, this is faster than calling ispseudoprime() only when n ends in 1 or 7, even when much larger N's are considered, e.g., up to 3000. - _M. F. Hasler_, Apr 14 2024)
%o A120819 (Python)
%o A120819 from sympy import isprime
%o A120819 L = ['8901', '234567']; s = '1234567'; c = len(s); m = 0
%o A120819 while c < 18881:
%o A120819 s += L[m%2]; c = len(s); m += 1
%o A120819 if isprime(int(s)): print(c, end = ', ') # _Ya-Ping Lu_, Jan 24 2025
%Y A120819 Cf. A006055, A057137, A120828, A120820, A120821, A120822, A120823, A120824, A120825, A120826, A120827.
%K A120819 nonn,base,hard,more
%O A120819 1,1
%A A120819 _Robert G. Wilson v_, Jul 05 2006
%E A120819 a(6) from _Arjen Lenstra_, Feb 20 2012