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A278038
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Binary vectors not containing three consecutive 1's; or, representation of n in the tribonacci base.
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43
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0, 1, 10, 11, 100, 101, 110, 1000, 1001, 1010, 1011, 1100, 1101, 10000, 10001, 10010, 10011, 10100, 10101, 10110, 11000, 11001, 11010, 11011, 100000, 100001, 100010, 100011, 100100, 100101, 100110, 101000, 101001, 101010, 101011, 101100, 101101, 110000, 110001, 110010, 110011, 110100, 110101, 110110, 1000000
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OFFSET
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0,3
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COMMENTS
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These are the nonnegative numbers written in the tribonacci numbering system.
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LINKS
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L. Carlitz, Richard Scoville, and V. E. Hoggatt, Jr., Fibonacci Representations of Higher Order, Part 2, The Fibonacci Quarterly, Vol. 10, No. 1 (1972), pp. 43-69, 94.
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EXAMPLE
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The tribonacci numbers (as in A000073(n), for n >= 3) are 1, 2, 4, 7, 13, 24, 44, 81, ... In terms of this base, 7 is written 1000, 8 is 1001, 11 is 1100, 12 is 1101, 13 is 10000, etc. Zero is 0.
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MAPLE
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# maximum index in A73 such that A73 <= n.
A73floorIdx := proc(n)
local k ;
for k from 3 do
return k ;
return k -1 ;
end if ;
end do:
end proc:
local k, L, nres ;
if n = 0 then
0;
else
k := A73floorIdx(n) ;
L := [1] ;
while k >= 4 do
k := k-1 ;
L := [1, op(L)] ;
else
L := [0, op(L)] ;
end if ;
end do:
add( op(i, L)*10^(i-1), i=1..nops(L)) ;
end if;
end proc:
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MATHEMATICA
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t[1] = 1; t[2] = 2; t[3] = 4; t[n_] := t[n] = t[n - 1] + t[n - 2] + t[n - 3]; a[n_] := Module[{s = {}, m = n, k}, While[m > 0, k = 1; While[t[k] <= m, k++]; k--; AppendTo[s, k]; m -= t[k]; k = 1]; FromDigits @ IntegerDigits[Total[2^(s - 1)], 2]]; Array[a, 100, 0] (* Amiram Eldar, Mar 04 2022 *)
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CROSSREFS
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See A003726 for the decimal representations of these binary strings.
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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