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 A259849 #37 Aug 28 2015 17:26:14 %S A259849 17,262,4312,16779232,4311709696,73014280192,1152921572789321728, %T A259849 1329227995784915873480267812046897152, %U A259849 95780971304118054976624684827067691392844968751005696 %N A259849 Average of consecutive pairs of perfect numbers. %C A259849 Assuming that no odd perfect number exists. %F A259849 a(n) = (A000396(n)+A000396(n+1))/2, assuming there are no odd perfect numbers. %e A259849 a(1) = (6 + 28)/2 = 17. %p A259849 perf:= n -> numtheory:-mersenne([n])*(numtheory:-mersenne([n])+1)/2: %p A259849 seq((perf(n)+perf(n+1))/2, n=1..15); # _Robert Israel_, Aug 20 2015 %Y A259849 Cf. A000396. %K A259849 nonn %O A259849 1,1 %A A259849 _José de Jesús Camacho Medina_, Aug 17 2015