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

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A054791 Earliest sequence with a(a(n))=n^2. 2
0, 1, 3, 4, 9, 6, 25, 8, 49, 16, 11, 100, 13, 144, 15, 196, 81, 18, 289, 20, 361, 22, 441, 24, 529, 36, 27, 676, 29, 784, 31, 900, 33, 1024, 35, 1156, 625, 38, 1369, 40, 1521, 42, 1681, 44, 1849, 46, 2025, 48, 2209, 64, 51, 2500, 53, 2704, 55, 2916, 57, 3136, 59 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

T. D. Noe, Table of n, a(n) for n=0..1000

Index entries for sequences of the a(a(n)) = 2n family

FORMULA

if n is a square then a(n)=a(sqrt(n))^2, otherwise if the difference between n and the highest square less than n is odd then a(n)=n+1, otherwise a(n)=(n-1)^2

MATHEMATICA

a[n_] := a[n] = Which[r = Sqrt[n]; IntegerQ[r], a[r]^2, OddQ[n - Floor[r]^2], n+1, True, (n-1)^2]; a[0]=0; a[1]=1; Table[a[n], {n, 0, 58}] (* Jean-Fran├žois Alcover, Aug 07 2012, after formula *)

PROG

(Haskell)

a054791 n = a054791_list `genericIndex` n

a054791_list = 0 : 1 : f 2 where

   f x | r ^ 2 == x  = a054791 r ^ 2 : f (x + 1)

       | odd (x - r) = x + 1         : f (x + 1)

       | otherwise   = (x - 1) ^ 2   : f (x + 1)

       where r = a000196 x

-- Reinhard Zumkeller, Oct 27 2013

CROSSREFS

Cf. A002516.

Sequence in context: A157020 A180253 A055225 * A167531 A062319 A178590

Adjacent sequences:  A054788 A054789 A054790 * A054792 A054793 A054794

KEYWORD

nice,nonn

AUTHOR

Henry Bottomley, Apr 27 2000

STATUS

approved

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

Content is available under The OEIS End-User License Agreement .

Last modified November 20 15:32 EST 2014. Contains 249751 sequences.