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 A101958 #13 Jan 17 2019 13:44:06 %S A101958 0,3,6,11,29,93,177,195,563,1800,3519,3537,8232,35160,37404,42329, %T A101958 70050,90791 %N A101958 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 13 for n > 0. %C A101958 Numbers n such that (220*10^n - 13)/9 is prime. %C A101958 Numbers n such that digit 2 followed by n >= 0 occurrences of digit 4 followed by digit 3 is prime. %C A101958 Numbers corresponding to terms <= 563 are certified primes. %C A101958 With changed signs, expansion of sinh(atan(x)). %C A101958 Next term after 3537 is greater than 5000. - _Ryan Propper_, Jun 16 2005 %C A101958 a(19) > 10^5. - _Robert Price_, Mar 16 2015 %D A101958 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. %H A101958 Makoto Kamada, <a href="https://stdkmd.net/nrr/2/24443.htm#prime">Prime numbers of the form 244...443</a>. %H A101958 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %F A101958 a(n) = A102953(n) - 1. %e A101958 24443 is prime, hence 3 is a term. %o A101958 (PARI) a=23;for(n=0,2000,if(isprime(a),print1(n,","));a=10*a+13) %o A101958 (PARI) for(n=0,2000,if(isprime((220*10^n-13)/9),print1(n,","))) %Y A101958 Cf. A000533, A002275, A102953. %K A101958 nonn,hard,more %O A101958 1,2 %A A101958 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004 %E A101958 2 more terms from _Ryan Propper_, Jun 16 2005 %E A101958 8232 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007 %E A101958 a(14)-a(18) derived from A102953 by _Robert Price_, Mar 16 2015