login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A057755 Number of digits in n-th Fermat number (A000215). 2
1, 1, 2, 3, 5, 10, 20, 39, 78, 155, 309, 617, 1234, 2467, 4933, 9865, 19729, 39457, 78914, 157827, 315653, 631306, 1262612, 2525223, 5050446, 10100891, 20201782, 40403563, 80807125, 161614249, 323228497, 646456994, 1292913987, 2585827973 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

REFERENCES

John H. Conway and R. K. Guy, The Book of Numbers, Copernicus, an imprint of Springer-Verlag, NY, 1995, page 139.

LINKS

Table of n, a(n) for n=0..33.

R. Mestrovic, Euclid's theorem on the infinitude of primes: a historical survey of its proofs (300 BC--2012) and another new proof, arXiv preprint arXiv:1202.3670, 2012 - From N. J. A. Sloane, Jun 13 2012

Eric Weisstein's World of Mathematics, Fermat Number

FORMULA

a(n) = floor(lg(F_n)+1) (F_n is the n-th Fermat number) [From Ivan Panchenko, Sep 06 2009]

EXAMPLE

a(6) = 20 because 2^(2^6) + 1 = 18446744073709551617 which is a twenty digit number.

MAPLE

seq(length(2^(2^n)), n=0..20); - Zerinvary Lajos, Apr 20 2008

MATHEMATICA

Table[ Floor[ 2^n * N[ Log[ 10, 2 ], 24 ] + 1 ], {n, 0, 43} ]

CROSSREFS

Cf. A000215.

Sequence in context: A105369 A047101 A251703 * A262482 A257113 A076834

Adjacent sequences:  A057752 A057753 A057754 * A057756 A057757 A057758

KEYWORD

nonn,base

AUTHOR

Robert G. Wilson v, Oct 30 2000

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified April 25 08:23 EDT 2017. Contains 285348 sequences.