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A059918
a(n) = (3^(2^n)-1)/2.
4
1, 4, 40, 3280, 21523360, 926510094425920, 1716841910146256242328924544640, 5895092288869291585760436430706259332839105796137920554548480
OFFSET
0,2
COMMENTS
Denominator of b(n) where b(n) = 1/2*(b(n-1) + 1/b(n-1)), b(0)=2. - Vladeta Jovovic, Aug 15 2002
LINKS
FORMULA
a(n) = a(n-1)*(3^(2^(n-1))+1) with a(0) = 1.
a(n) = (3^(2^n)-1)/2 = (A059723(n+1)-A059723(n))/A059723(n) = A059917(n)-1 = a(n-1)*A059919(n-1) = a(n-1)*(A011764(n-1)+1)
1 = Sum_{n>=0} 3^(2^n)/a(n+1). 1 = 3/4 + 9/40 + 81/3280 + 6561/21523360 + ...; with partial sums: 3/4, 39/40, 3279/3280, 21523359/21523360, ..., (a(n)-1)/a(n), ... . - Gary W. Adamson, Jun 22 2003
A136308(n) = A007089(a(n)). - Jason Kimberley, Dec 19 2012
MATHEMATICA
Array[(3^(2^#) - 1)/2 &, 8, 0] (* Michael De Vlieger, Feb 05 2022 *)
PROG
(PARI) { for (n=0, 11, write("b059918.txt", n, " ", (3^(2^n) - 1)/2); ) } \\ Harry J. Smith, Jun 30 2009
CROSSREFS
Cf. A059917 (numerators).
Sequence in context: A303124 A072445 A000841 * A375141 A296101 A002677
KEYWORD
nonn,easy
AUTHOR
Henry Bottomley, Feb 08 2001
STATUS
approved