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A055236
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Sums of two powers of 4.
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0
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2, 5, 8, 17, 20, 32, 65, 68, 80, 128, 257, 260, 272, 320, 512, 1025, 1028, 1040, 1088, 1280, 2048, 4097, 4100, 4112, 4160, 4352, 5120, 8192, 16385, 16388, 16400, 16448, 16640, 17408, 20480, 32768, 65537, 65540, 65552, 65600, 65792, 66560, 69632, 81920
(list; table; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| a(n) = 4^(n-trinv(n))+4^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)=4^n+4^k, so as a sequence a(n) = 4^A002262(n)+4^A003056(n).
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EXAMPLE
| a(4) = 20 = 4^2+4^1
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MATHEMATICA
| t = 4^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.
Sequence in context: A048237 A048139 A071085 * A103041 A176223 A006827
Adjacent sequences: A055233 A055234 A055235 * A055237 A055238 A055239
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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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