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 A119973 #15 Feb 09 2023 05:01:23 %S A119973 21,33,42,57,66,69,77,84,93,105,114,129,132,133,138,141,154,161,165, %T A119973 168,177,186,189,201,209,210,213,217,228,237,249,253,258,264,266,273, %U A119973 276,282,285,297,301,308,309,321,322,329,330,336,341,345,354,357,372 %N A119973 Numbers of the form (4k+1)*2^j which are not a sum of two squares. %C A119973 Intersection of A091072 and A022544. - _Robert Israel_, Oct 28 2018 %H A119973 Robert Israel, <a href="/A119973/b119973.txt">Table of n, a(n) for n = 1..10000</a> %e A119973 42 is there because it's (4*5+1)*2^1 and is not a sum of two squares. %p A119973 filter:= proc(n) local w; w:= n/2^padic:-ordp(n,2); %p A119973 w mod 4 = 1 and select(t -> t[2]::odd and t[1] mod 4 = 3, ifactors(w)[2]) <> [] %p A119973 end proc: %p A119973 select(filter, [$1..1000]); # _Robert Israel_, Oct 28 2018 %t A119973 okQ[n_] := EvenQ[(n/2^IntegerExponent[n, 2]-1)/2] && SquaresR[2, n] == 0; %t A119973 Select[Range[1000], okQ] (* _Jean-François Alcover_, Feb 09 2023 *) %Y A119973 Cf. A001481, A022544, A084109, A091072, A120772. %K A119973 easy,nonn %O A119973 1,1 %A A119973 _Alford Arnold_, Jun 03 2006 %E A119973 More terms from _Don Reble_, Jul 24 2006