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%I #14 Dec 31 2017 12:28:45
%S 2,8,14,50,56,98,344,350,392,686,2402,2408,2450,2744,4802,16808,16814,
%T 16856,17150,19208,33614,117650,117656,117698,117992,120050,134456,
%U 235298,823544,823550,823592,823886,825944,840350,941192,1647086,5764802,5764808
%N Sums of two powers of 7.
%H T. D. Noe, <a href="/A055258/b055258.txt">Rows n = 0..100 of triangle, flattened</a>
%F a(n) = 7^(n-trinv(n))+7^trinv(n), where trinv(n) = floor((1+sqrt(1+8*n))/2) = A002262(n) and n-trinv(n) = A003056(n)
%F Regarded as a triangle T(n, k) = 7^n + 7^k, so as a sequence a(n) = 7^A002262(n) + 7^A003056(n).
%t t = 7^Range[0, 9]; Select[Union[Flatten[Table[i + j, {i, t}, {j, t}]]], # <= t[[-1]] + 1 &] (* _T. D. Noe_, Oct 09 2011 *)
%t Total/@Tuples[7^Range[0,10],2]//Union (* _Harvey P. Dale_, Dec 31 2017 *)
%Y Cf. A052216.
%Y Equals 2*A073218.
%K easy,nonn,tabl
%O 0,1
%A _Henry Bottomley_, Jun 22 2000
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