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 A047981 #11 Oct 15 2013 22:30:21
%S A047981 3,7,17,71,19,59,167,757,197,159,799,227,317,415,361,521,3289,2633,
%T A047981 1637,1861,1691,1997,2053,4097,6437,5731,9199,11603,5641,3833,26885,
%U A047981 6637,26815,32117,18637,29933,31667,5227,19891,47303,54973,5207,59537
%N A047981 a(n) = A047980(2n).
%H A047981 <a href="/index/Pri#primes_AP">Index entries for sequences related to primes in arithmetic progressions</a>
%F A047981 a(n) = min {k}: A034693(a(n)) is an even number such that in a(n)*k+1 progression the first prime occurs at even 2n=k position.
%e A047981 First example: a(1)=3 since in 3k+1 sequence, the first term is 3, a prime and the d=2 is the smallest such difference. The next such progression is 5k+1 because 5*2+1=11 is prime. 2nd example: here at n=6 a(6)=59. This means that 2n=12 occurs first in A034693 at its position 59, which means that its first prime is 12*59+1=709. arises as 12th term (such progressions are: 59k+1,85k+1,133k+1, etc.)
%Y A047981 Cf. A047980, A047982, A034693, A034782 - A034784.
%K A047981 nonn
%O A047981 1,1
%A A047981 _Labos Elemer_