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A359500
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a(n) = (7^2^n - 1)/2^(n+3).
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1
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3, 75, 90075, 259632270075, 4314170602515315024630075, 2382344702413741601833152075318304337413311121350075, 1452944967966417671787414728262962471027692106596483349510252251060925112718067382475349181570930962790075
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n)/a(n-1) = (7^2^(n-1) + 1)/2 = 2^(n+1) * a(n-1) + 1.
For all n > m, a(n) and a(m) are congruent modulo 2^(m+2) but not modulo 2^(m+3).
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PROG
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(PARI) a(n) = (7^2^n - 1)/2^(n+3)
(Python)
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CROSSREFS
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Cf. {odd part of m^2^n - 1}: A068531 (m=3 or m=9), A097421 (m=5), this sequence (m=7).
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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