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A325907
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a(n) = ( (-1)^n * Sum_{k=0..n-2} (-1)^k*10^(2^k) + 10^(2^(n-1)) - ((-1)^n+3)/2 )/3.
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7
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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a(n) = -a(n-1) - 1 + A093137(2^(n-2)) * 10^(2^(n-2)).
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EXAMPLE
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36 = -3 - 1 + 4 * 10^1.
3363 = -36 - 1 + 34 * 10^2.
33336636 = -3363 - 1 + 3334 * 10^4.
3333333366663363 = -33336636 - 1 + 33333334 * 10^8.
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T(n) = n*(n+1)/2.
T(3) = 6.
T(36) = 666.
T(3363) = 5656566.
T(33336636) = 555665666566566.
T(3333333366663363) = 5555555666655656666556566566566.
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MATHEMATICA
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a[n_] := ((-1)^n * Sum[(-1)^k * 10^(2^k), {k, 0, n - 2}] + 10^(2^(n - 1)) - ((-1)^n + 3)/2)/3; Array[a, 7] (* Amiram Eldar, May 07 2021 *)
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PROG
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(PARI) {a(n) = ((-1)^n*sum(k=0, n-2, (-1)^k*10^2^k)+10^2^(n-1)-((-1)^n+3)/2)/3}
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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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