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 A002238 M0825 N0314 #38 Dec 24 2021 02:30:20 %S A002238 1,2,3,7,10,13,18,27,37,51,74,157,271,458,530,891,1723,1793,1849,1986, %T A002238 2191,2869,4993,7777,11730,15313,29171,35899,36227,71570,199219, %U A002238 233914,297499,332523,348547,538657,986130,999599 %N A002238 Numbers k such that 21*2^k - 1 is prime. %D A002238 H. Riesel, Lucasian criteria for the primality of N=h.2^n-1, Math. Comp., 23 (1969), 869-875. %D A002238 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). %D A002238 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A002238 Ray Ballinger and Wilfrid Keller, <a href="http://www.prothsearch.com/riesel1.html">List of primes k.2^n + 1 for k < 300</a> %H A002238 R. K. Guy, <a href="/A005165/a005165.pdf">The strong law of small numbers</a>. Amer. Math. Monthly 95 (1988), no. 8, 697-712. [Annotated scanned copy] %H A002238 Wilfrid Keller, <a href="http://www.prothsearch.com/riesel2.html">List of primes k.2^n - 1 for k < 300</a> %H A002238 Kosmaj, <a href="http://www.15k.org/riesellist.html">Riesel list k<300</a>. %H A002238 <a href="/index/Pri#riesel">Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime</a> %o A002238 (PARI) is(n)=ispseudoprime(21*2^n-1) \\ _Charles R Greathouse IV_, May 22 2017 %Y A002238 Cf. A032360, 21*2^k + 1 is prime. %K A002238 hard,nonn %O A002238 1,2 %A A002238 _N. J. A. Sloane_ %E A002238 More terms from _Hugo Pfoertner_, Jun 22 2004 %E A002238 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008