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 A101155 #16 Jan 17 2019 13:44:06 %S A101155 0,2,4,5,9,11,12,38,47,53,63,81,146,147,359,398,1637,1875,2145,2193, %T A101155 15788,23073,38465,68399 %N A101155 Indices of primes in sequence defined by A(0) = 73, A(n) = 10*A(n-1) + 63 for n > 0. %C A101155 Numbers n such that (720*10^n - 63)/9 is prime. %C A101155 Numbers n such that digit 7 followed by n >= 0 occurrences of digit 9 followed by digit 3 is prime. %C A101155 Numbers corresponding to terms <= 398 are certified primes. %C A101155 a(25) > 2*10^5. - _Robert Price_, Nov 11 2015 %D A101155 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. %H A101155 Makoto Kamada, <a href="https://stdkmd.net/nrr/7/79993.htm#prime">Prime numbers of the form 799...993</a>. %H A101155 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %F A101155 a(n) = A099190(n) - 1. %e A101155 7999993 is prime, hence 5 is a term. %t A101155 Select[Range[0, 100000], PrimeQ[(720*10^# - 63)/9] &] (* _Robert Price_, Nov 11 2015 *) %o A101155 (PARI) a=73;for(n=0,1000,if(isprime(a),print1(n,","));a=10*a+63) %o A101155 (PARI) for(n=0,1000,if(isprime((720*10^n-63)/9),print1(n,","))) %Y A101155 Cf. A000533, A002275, A101849, A169830, A099190. %K A101155 nonn,hard,more %O A101155 1,2 %A A101155 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004 %E A101155 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 %E A101155 a(21)-a(24) from Kamada data by _Ray Chandler_, Apr 30 2015