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 A031938 #22 Aug 10 2025 19:49:33
%S A031938 887,1637,3089,3413,3947,5717,5903,5987,6803,7649,8243,8543,8783,8867,
%T A031938 9257,10223,10433,10667,11027,11093,11177,11447,11597,11657,11867,
%U A031938 11987,13127,13421,13649,14087,14177,15473,16943,17519,17807,18149,18461,18617,18839
%N A031938 Lower prime of a difference of 20 between consecutive primes.
%H A031938 Remi Eismann, <a href="/A031938/b031938.txt">Table of n, a(n) for n = 1..10000</a>
%H A031938 <a href="/index/Pri#gaps">Index entries for primes, gaps between</a>
%F A031938 a(n) = prime(A320708(n)). - _R. J. Mathar_, Apr 30 2024
%e A031938 887 is a term as the next prime is 907.
%t A031938 (*M6*) a=887; S={}; Do[b=NextPrime[a]; If[b-a==20,AppendTo[S,a]]; a=b,{10^4}]; S (* _Zak Seidov_, Aug 14 2009 *)
%t A031938 Transpose[Select[Partition[Prime[Range[2000]], 2, 1], Last[#] - First[#] == 20 &]][[1]] (* _Bruno Berselli_, Apr 09 2013 *)
%o A031938 (Magma) [p: p in PrimesUpTo(20000) | NextPrime(p)-p eq 20]; // _Bruno Berselli_, Apr 09 2013
%K A031938 nonn
%O A031938 1,1
%A A031938 _Jeff Burch_
%E A031938 Entries and b-file checked by _Zak Seidov_, Aug 14 2009