%I A077021
%S A077021 1,3,5,1,11,9,13,31,5,57,67,47,181,87,275,449,101,999,797,1201,2795,
%T A077021 393,5197,5983,4411,16377,7555,25199,40309,10089,90707,70529,110885,
%U A077021 251943,30173,473713,534059,413367,1481485,654751,2308219,3617721
%N A077021 a(n) is the unique odd positive solution y of 2^n = 7x^2+y^2.
%D A077021 A. Engel, Problem-Solving Strategies. p. 126.
%H A077021 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               DiophantineEquation2ndPowers.html">Diophantine Equations 2nd Powers</
               a>
%F A077021 A077021(n+1)=Abs[A002249(n)] [From Artur Jasinski (grafix(AT)csl.pl), 
               Oct 05 2008]
%t A077021 a = {}; Do[k = Expand[((1 + I Sqrt[7])/2)^n + ((1 - I Sqrt[7])/2)^n]; 
               AppendTo[a, Abs[k]], {n, 1, 50}]; a [From Artur Jasinski (grafix(AT)csl.pl), 
               Oct 05 2008]
%Y A077021 Cf. A077020.
%Y A077021 a(n)=abs(A002249(n)).
%Y A077021 Sequence in context: A101035 A026253 A138259 this_sequence A143250 A084833 
               A069111
%Y A077021 Adjacent sequences: A077018 A077019 A077020 this_sequence A077022 A077023 
               A077024
%K A077021 nonn
%O A077021 1,2
%A A077021 Ed Pegg Jr. (ed(AT)mathpuzzle.com), Oct 17, 2002