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 A101727 #17 Jan 17 2019 13:44:06 %S A101727 0,1,3,4,12,21,24,27,37,66,141,283,294,379,396,1216,1639,2884,3285, %T A101727 7734,29305 %N A101727 Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) - 13 for n > 0. %C A101727 Numbers n such that (410*10^n + 13)/9 is prime. %C A101727 Numbers n such that digit 4 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime. %C A101727 Numbers corresponding to terms <= 396 are certified primes. %C A101727 a(22) > 10^5. - _Robert Price_, May 22 2015 %D A101727 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. %H A101727 Makoto Kamada, <a href="https://stdkmd.net/nrr/4/45557.htm#prime">Prime numbers of the form 455...557</a>. %H A101727 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %F A101727 a(n) = A102992(n) - 1. %e A101727 457 is prime, hence 1 is a term. %t A101727 Select[Range[0, 1000], PrimeQ[(410*10^# + 13)/9] &] (* _Robert Price_, May 22 2015 *) %o A101727 (PARI) a=47;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-13) %o A101727 (PARI) for(n=0,1500,if(isprime((410*10^n+13)/9),print1(n,","))) %Y A101727 Cf. A000533, A002275, A102992. %K A101727 nonn,hard,more %O A101727 1,3 %A A101727 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004 %E A101727 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 %E A101727 a(21) from Kamada data by _Ray Chandler_, Apr 30 2015