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A055258
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Sums of two powers of 7.
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1
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2, 8, 14, 50, 56, 98, 344, 350, 392, 686, 2402, 2408, 2450, 2744, 4802, 16808, 16814, 16856, 17150, 19208, 33614, 117650, 117656, 117698, 117992, 120050, 134456, 235298, 823544, 823550, 823592, 823886, 825944, 840350, 941192, 1647086, 5764802, 5764808
(list; table; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| 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)
Regarded as a triangle T(n, k)=7^n+7^k, so as a sequence a(n) =7^A002262(n)+7^A003056(n).
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EXAMPLE
| a(4) = 56 = 7^2+7^1
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MATHEMATICA
| t = 7^Range[0, 9]; Select[Union[Flatten[Table[i + j, {i, t}, {j, t}]]], # <= t[[-1]] + 1 &] (* T. D. Noe, Oct 09 2011 *)
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CROSSREFS
| Cf. A052216.
Equals 2*A073218.
Sequence in context: A039660 A119752 A111001 * A192777 A054981 A059449
Adjacent sequences: A055255 A055256 A055257 * A055259 A055260 A055261
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KEYWORD
| easy,nonn,tabl
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AUTHOR
| Henry Bottomley (se16(AT)btinternet.com), Jun 22 2000
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