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A014980 Start with 5. Multiply the two numbers closest to n/2 to get the next number. 3
5, 6, 9, 20, 100, 2500, 1562500, 610351562500, 93132257461547851562500, 2168404344971008868014905601739883422851562500, 1175494350822287507968736537222245677818665556772087521508751706278417259454727172851562500 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

More precisely, a(n+1) = floor(a(n)/2) * ceiling(a(n)/2), a(0) = 5.

A194079(n) gives number of digits of a(n).

LINKS

Table of n, a(n) for n=0..10.

FORMULA

a(0) = 5; a(k+1) = floor(a(k)/2) * ceiling(a(k)/2).

a(n+1) = A002620(a(n)), a(0) = 5. - Reinhard Zumkeller, Oct 12 2011

EXAMPLE

6 = 2*3; 9 = 3*3; 20 = 4*5; ...

MATHEMATICA

a=5; a=Table[a=Ceiling[a/2]*Floor[a/2], {n, 0, 10}] (* Vladimir Joseph Stephan Orlovsky, Apr 13 2010 *)

NestList[Floor[#/2]Ceiling[#/2]&, 5, 10] (* Harvey P. Dale, Jul 10 2012 *)

PROG

(Haskell)

a014980 n = a014980_list !! n

a014980_list = iterate a002620 5

-- Reinhard Zumkeller, Oct 12 2011

CROSSREFS

Cf. A002620, A194079.

Sequence in context: A124519 A154311 A279702 * A066901 A273039 A019125

Adjacent sequences:  A014977 A014978 A014979 * A014981 A014982 A014983

KEYWORD

nonn,nice,easy

AUTHOR

Colin Sandon (sandon(AT)together.net)

EXTENSIONS

More terms from James A. Sellers, Feb 05 2000

STATUS

approved

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Last modified February 20 07:06 EST 2018. Contains 299359 sequences. (Running on oeis4.)