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 A101952 #26 Jan 17 2019 13:44:06 %S A101952 0,4,24,454,760,9204,13560,15954,26668,113940 %N A101952 Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 81 for n > 0. %C A101952 Numbers n such that 20*10^n + 9 is prime. %C A101952 Numbers n such that digit 2 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime. %C A101952 Numbers corresponding to terms <= 760 are certified primes. %C A101952 a(11) > 2*10^5. - _Robert Price_, Jun 06 2015 %D A101952 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. %H A101952 Makoto Kamada, <a href="https://stdkmd.net/nrr/2/20009.htm#prime">Prime numbers of the form 200...009</a>. %F A101952 a(n) = A101392(n-1) - 1. - _Robert Price_, Nov 25 2014 %e A101952 200009 is prime, hence 4 is a term. %t A101952 Select[Range[0, 300], PrimeQ[20*10^# + 9] &] (* _Robert Price_, Jun 06 2015 *) %o A101952 (PARI) a=29;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-81) %o A101952 (PARI) for(n=0,1500,if(isprime(20*10^n+9),print1(n,","))) %Y A101952 Cf. A000533, A002275, A101392. %K A101952 nonn,hard,more %O A101952 1,2 %A A101952 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004 %E A101952 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 %E A101952 a(9)-a(10) derived from A101392 by _Robert Price_, Nov 25 2014