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 A242218 #8 May 08 2014 16:52:19 %S A242218 511,537,1073,1461,1501,1541,1763,2071,2181,2449,4101,4387,4399,4467, %T A242218 4559,4607,4681,4705,5089,5257,5429,6415,6621,6671,7097,7111,7261, %U A242218 7391,7447,7811,7831,7897,7909,7969,8079,8129,8193,8333,8639,8915,9101,9113,9123,9211 %N A242218 Semiprimes which are the arithmetic mean of three consecutive primes. %H A242218 K. D. Bajpai, <a href="/A242218/b242218.txt">Table of n, a(n) for n = 1..10000</a> %e A242218 a(1) = 511 = (503 + 509 + 521)/3 = 7 * 73 is semiprime. %e A242218 a(2) = 537 = (523 + 541 + 547)/3 = 3 * 179 is semiprime. %p A242218 with(numtheory): A242218:= proc()local k ; k:=(ithprime(x)+ithprime(x+1)+ithprime(x+2))/3; if k=floor(k) and bigomega(k)=2 then RETURN (k); fi; end: seq(A242218 (),x=2..2000); %o A242218 (PARI) for(k=1, 2000, t=prime(k)+prime(k+1)+prime(k+2); if(t%3==0 && bigomega(t/3)==2, print1(t/3, ", "))) \\ _Colin Barker_, May 08 2014 %Y A242218 Cf. A001358, A133529, A216432, A234297. %K A242218 nonn %O A242218 1,1 %A A242218 _K. D. Bajpai_, May 07 2014