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 A101826 #18 Jan 17 2019 13:44:06
%S A101826 0,1,217,691,1804,2206,2872,59134
%N A101826 Indices of primes in sequence defined by A(0) = 37, A(n) = 10*A(n-1) - 53 for n > 0.
%C A101826 Numbers n such that (280*10^n + 53)/9 is prime.
%C A101826 Numbers n such that digit 3 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime.
%C A101826 Numbers corresponding to terms <= 691 are certified primes.
%D A101826 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H A101826 Makoto Kamada, <a href="https://stdkmd.net/nrr/3/31117.htm#prime">Prime numbers of the form 311...117</a>.
%H A101826 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A101826 a(n) = A101393(n) - 1.
%e A101826 317 is prime, hence 1 is a term.
%t A101826 nn=2900;Transpose[Select[Thread[{NestList[10#-53&,37,nn], Range[0,nn]}], PrimeQ[First[#]]&]] [[2]] (* _Harvey P. Dale_, Mar 26 2011 *)
%o A101826 (PARI) a=37;for(n=0,2000,if(isprime(a),print1(n,","));a=10*a-53)
%o A101826 (PARI) for(n=0,2000,if(isprime((280*10^n+53)/9),print1(n,",")))
%Y A101826 Cf. A000533, A002275, A101393.
%K A101826 nonn,hard,more
%O A101826 1,3
%A A101826 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
%E A101826 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E A101826 a(8) derived from A101393 by _Robert Price_, Jan 26 2015