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 A101848 #15 Jan 17 2019 13:44:06 %S A101848 0,16,18,28,42,118,172,948,1608,5578,19678,34146,43492,97798 %N A101848 Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 81 for n > 0. %C A101848 Numbers n such that (360*10^n - 81)/9 is prime. %C A101848 Numbers n such that digit 3 followed by n >= 0 occurrences of digit 9 followed by digit 1 is prime. %C A101848 Numbers corresponding to terms <= 948 are certified primes. %C A101848 a(15) > 10^5. - _Robert Price_, Mar 17 2015 %D A101848 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. %H A101848 Makoto Kamada, <a href="https://stdkmd.net/nrr/3/39991.htm#prime">Prime numbers of the form 399...991</a>. %H A101848 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %F A101848 a(n) = A101396(n) - 1. %e A101848 31 is prime, hence 0 is a term. %t A101848 Select[Range[0, 1000], PrimeQ[(360*10^# - 81)/9] &] (* _Robert Price_, Mar 17 2015 *) %o A101848 (PARI) a=31;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+81) %o A101848 (PARI) for(n=0,1500,if(isprime((360*10^n-81)/9),print1(n,","))) %Y A101848 Cf. A000533, A002275, A101396. %K A101848 nonn,hard,more %O A101848 1,2 %A A101848 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004 %E A101848 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 %E A101848 a(12)-a(14) derived from A101396 by _Robert Price_, Mar 17 2015