A250482 - OEIS

%I #21 Nov 27 2014 03:33:31

%S 1,2,3,4,5,6,8,9,10,11,12,13,16,17,18,20,24,25,26,27,29,32,33,36,37,

%T 38,40,41,44,48,50,51,52,53,57,64,65,66,68,72,73,80,81,82,83,85,89,96,

%U 97,100,101,102,104,108,113,116,122,123,125,128,129,132,137,144

%N Numbers of the form 2^x + y^2, with x and y >=0.

%C No terms are congruent to 7 mod 8: subsequence of A004777.

%H Vincenzo Librandi, <a href="/A250482/b250482.txt">Table of n, a(n) for n = 1..2500</a>

%e 12 is in this sequence because 2^3+2^2 = 12.

%e 51 is in this sequence because 2^1+7^2 = 51.

%t nn=15; Union[Select[Flatten[Table[2^x + y^2, {x, 0, nn}, {y, 0, nn}]], # <=nn^2 &]]

%o (PARI) isok(n) = {k=0; while (2^k <= n, if (issquare(n - 2^k), return(1)); k++;); return (0);} \\ _Michel Marcus_, Nov 24 2014

%Y Cf. A004777, A250481.

%Y Cf. sequences of the type k^x+y^k: this sequence (k=2), A250483 (k=3), A250545 (k=4), A250546 (k=5), A250547 (k=6), A250715 (k=7).

%K nonn

%O 1,2

%A _Vincenzo Librandi_, Nov 24 2014