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A173019
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a(n) is the value of row n in triangle A083093 seen as ternary number.
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4
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1, 4, 16, 28, 112, 448, 784, 3136, 12301, 19684, 78736, 314944, 551152, 2204608, 8818432, 15432256, 61729024, 242132884, 387459856, 1549839424, 6199180549, 10848875968, 43395503872, 173577055372, 303766932781, 1215067731124
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OFFSET
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0,2
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COMMENTS
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Previous name was "Pascal's Triangle mod 3 converted to decimal."
If 2|a(n), then 4|a(n).
If 8|a(n), then 16|a(n).
If a(n)=4*a(n-1), then 3 does not divide n.
The first few odd values for a(n) are a(0)=1, a(8)=12301, a(20)=6199180549, a(24)=303766932781.
It appears that, as the terms of A001317 (analogous to this sequence, using binary instead of ternary) can be uniquely represented as products of Fermat numbers, the terms of this sequence can be represented as products from a nontrivial set of numbers. - Thomas Anton, Oct 27 2018
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LINKS
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FORMULA
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a(3^n) = 3^(3^n) + 1.
a(3^n) = (8*a((3^n)-1) + 12)/5. [5*a(3^n) = 1200...0012 (base 3), 8*a((3^n)-1) = (22)(1212...2121) = 11222...2202 (base 3).]
For n > 0, a((3^n)+1) = 4*a(3^n) and a((3^n)+2) = 4*a((3^n)+1).
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EXAMPLE
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a(9) = 3^(3^2) + 1 = 19684;
a(8) = (5*19684 - 12)/8 = 12301;
a(10) = 4*19684 = 78736.
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MATHEMATICA
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FromDigits[#, 3] & /@ Table[Mod[Binomial[n, k], 3], {n, 0, 25}, {k, 0, n}] (* Michael De Vlieger, Oct 31 2018 *)
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PROG
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(Haskell)
a173019 = foldr (\t v -> 3 * v + t) 0 . map toInteger . a083093_row
(PARI) a(n) = my(v = vector(n+1, k, binomial(n, k-1))); fromdigits(apply(x->x % 3, v), 3); \\ Michel Marcus, Nov 21 2018
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CROSSREFS
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Cf. A006940 (takes these values and converts them to decimal notation).
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KEYWORD
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base,easy,nonn
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AUTHOR
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Michael Thaler (michael_thaler(AT)brown.edu), Nov 07 2010
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EXTENSIONS
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a(13) and a(19) corrected and name clarified by Tom Edgar, Oct 11 2015
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STATUS
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approved
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