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a(n) = number of representations of A020670(n) as x^2 + 7*y^2.
1

%I #9 Nov 01 2014 20:48:10

%S 1,1,1,1,1,1,1,2,1,1,1,1,2,1,1,1,1,1,1,1,1,3,1,1,1,1,1,1,2,1,1,1,1,1,

%T 2,1,1,2,1,3,1,2,1,1,1,1,1,1,1,1,3,1,2,1,1,1,1,1,1,1,1,1,2,1,2,1,1,1,

%U 2,4,1,1,1,1,1,1,1,1,2,1,2,1,1,1,1,2,1,1,1,1,1,2,1,4,1,1,3,1,1,1,1

%N a(n) = number of representations of A020670(n) as x^2 + 7*y^2.

%C Among first 10000 terms, maximal value is 12 for n = 5875, 7320, 9211.

%C That is, numbers A020670(5875, 7320, 9211) = (32384, 40832, 52096) are expressible as x^2 + 7*y^2 in 12 ways. E.g., 32384 = x^2 + 7*y^2 for {x,y}= {4, 68}, {31, 67}, {53, 65}, {74, 62}, {94, 58}, {116, 52}, {122, 50}, {151, 37}, {164, 28}, {172, 20}, {178, 10}, {179, 7}.

%H Zak Seidov, <a href="/A249545/b249545.txt">Table of n, a(n) for n = 1..10000</a>

%Y Cf. A020670.

%K nonn

%O 1,8

%A _Zak Seidov_, Oct 31 2014