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 A304874 #10 May 20 2018 11:30:47 %S A304874 3,7,13,19,31,37,61,79,97,103,139,157,193,223,241,271,317,349,379,439, %T A304874 421,487,521,619,661,719,757,829,881,883,1009,1087,1063,1213,1291, %U A304874 1291,1429,1511,1579,1669,1741,1831,1879 %N A304874 Greatest prime p1 < p2 such that n^2 = (p1 + p2)/2 and p2 is prime. %C A304874 Each square > 1 can be written as the average of 2 primes p1 < p2. a(n) gives the greatest prime p1 such that n^2 = (p1 + p2) / 2. The corresponding p2 is provided in A304875. %H A304874 Hugo Pfoertner, <a href="/A304874/b304874.txt">Table of n, a(n) for n = 2..10000</a> %F A304874 a(n) = n^2 - A172989(n) = A304875(n) - 2*A172989(n). %e A304874 a(2) = 3 because 2^2 = 4 = (3 + 5)/2, %e A304874 a(7) = 37 because 7^2 = 49 = (37 + 61)/2 and none of the primes p1 = 41, 43 or 47 leads to a prime p2. %Y A304874 Cf. A172989, A304875. %K A304874 nonn %O A304874 2,1 %A A304874 _Hugo Pfoertner_, May 20 2018