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A299156
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Numbers k such that k*(k+1) divides tribonacci(k) (A000073(k)).
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1
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1, 256, 397, 1197, 8053, 8736, 9901, 32173, 33493, 33757, 38461, 48757, 56101, 57073, 64153, 76561, 79693, 87517, 100608, 102217, 105253, 105601, 105913, 105997, 107713, 108553, 110976, 116293, 123121, 131437, 138517, 143137, 147541, 151237, 156601, 171253
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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tribonacci(256) = 10285895715599251294835119279496333059462348558276025598603904254464 = 256 * 257 * 156339611436029476149609668037091638184921397104146789862048642.
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MAPLE
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with(LinearAlgebra[Modular]):
T:= (n, m)-> MatrixPower(m, Mod(m, <<0|1|0>,
<0|0|1>, <1|1|1>>, float[8]), n)[1, 3]:
a:= proc(n) option remember; local i, k, ok;
if n=1 then 1 else
for k from 1+a(n-1) do ok:= true;
for i in ifactors(k*(k+1))[2] while ok do
ok:= is(T(k, i[1]^i[2])=0)
od; if ok then break fi
od; k
fi
end:
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MATHEMATICA
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a = b = 0; c = d = 1; k = 2; lst = {1}; While[k < 171255, If[ Mod[c, k (k + 1)] == 0, AppendTo[lst, k]]; a = b; b = c; c = d; d = a + b + c; k++] (* Robert G. Wilson v, Feb 07 2018 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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