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A055237
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Sums of two powers of 5.
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1
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2, 6, 10, 26, 30, 50, 126, 130, 150, 250, 626, 630, 650, 750, 1250, 3126, 3130, 3150, 3250, 3750, 6250, 15626, 15630, 15650, 15750, 16250, 18750, 31250, 78126, 78130, 78150, 78250, 78750, 81250, 93750, 156250, 390626, 390630, 390650, 390750, 391250, 393750
(list; table; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| a(n) = 5^(n-trinv(n))+5^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)=5^n+5^k, so as a sequence a(n) =5^A002262(n)+5^A003056(n).
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EXAMPLE
| a(4) = 30 = 5^2+5^1
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MATHEMATICA
| t = 5^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: A188224 A104142 A079713 * A057434 A162581 A061547
Adjacent sequences: A055234 A055235 A055236 * A055238 A055239 A055240
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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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