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 A278647 #21 Dec 11 2016 06:55:44 %S A278647 5,3,2,2,3,5,1,3,1,4,1,2,2,1,1,4,5,1,1,1,2,3,2,1,4,3,2,3,1,1,3,2,2,3, %T A278647 2,2,1,1,4,2,3,1,1,2,1,1,3,1,1,2,2,1,1,2,1,2,1,2,5,5,1,1,3,3,2,1,2,1, %U A278647 1,3,2,1,1,2,1,4,1,4,1,3,1,1,3,2,1,1,1,2,2,3,3,1,1,2,3,2,1,1,1,3 %N A278647 First differences of Hypotenuse numbers A009003. %C A278647 a(n) <= 5, since A009003 contains all multiples of 5. - _Robert Israel_, Dec 08 2016 %H A278647 Robert Israel, <a href="/A278647/b278647.txt">Table of n, a(n) for n = 1..10000</a> %F A278647 a(n) = A009003(n+1) - A009003(n). %p A278647 L:= select(t -> has(numtheory:-factorset(t) mod 4,1), [$1..1000]): %p A278647 L[2..-1]-L[1..-2]; # _Robert Israel_, Dec 08 2016 %t A278647 Differences@ Select[Range@ 208, Length@ PowersRepresentations[#^2, 2, 2] > 1 &] (* _Michael De Vlieger_, Nov 25 2016, after _Alonso del Arte_ at A009003 *) %Y A278647 Cf. A009003. %K A278647 nonn %O A278647 1,1 %A A278647 _Zhandos Mambetaliyev_, Nov 24 2016