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A199115
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a(n) = 5*4^n+1.
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3
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6, 21, 81, 321, 1281, 5121, 20481, 81921, 327681, 1310721, 5242881, 20971521, 83886081, 335544321, 1342177281, 5368709121, 21474836481, 85899345921, 343597383681, 1374389534721, 5497558138881, 21990232555521, 87960930222081
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OFFSET
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0,1
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COMMENTS
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An Engel expansion of 4/5 to the base 4 as defined in A181565, with the associated series expansion 4/5 = 4/6 + 4^2/(6*21) + 4^3/(6*21*81) + 4^4/(6*21*81*321) + ... . Cf. A136412 and A140660. - Peter Bala, Oct 29 2013
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LINKS
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FORMULA
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a(n) = 4*a(n-1)-3.
a(n) = 5*a(n-1)-4*a(n-2).
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PROG
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(Magma) [5*4^n+1: n in [0..30]];
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CROSSREFS
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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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