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

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A026239 Beginning with the natural numbers, swap the k-th prime and k-th composite. 7
1, 4, 6, 2, 8, 3, 9, 5, 7, 11, 10, 13, 12, 17, 19, 23, 14, 29, 15, 31, 37, 41, 16, 43, 47, 53, 59, 61, 18, 67, 20, 71, 73, 79, 83, 89, 21, 97, 101, 103, 22, 107, 24, 109, 113, 127, 25, 131, 137, 139, 149, 151, 26, 157, 163, 167, 173, 179, 27, 181, 28, 191, 193, 197, 199 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Involution (self-inverse permutation) of [positive] natural numbers.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

Index entries for sequences that are permutations of the natural numbers

FORMULA

a(1) = 1 and a(n) = if n is prime then A002808(A049084(n)) else A000040(A066246(n)) for n>1. - Reinhard Zumkeller, Dec 13 2001

MATHEMATICA

Composite[n_Integer] := FixedPoint[n + PrimePi@# + 1 &, n + PrimePi@n + 1]; f[1] = 1; f[n_] := If[ PrimeQ@n, Composite@ PrimePi@n, Prime[n - 1 - PrimePi@n]]; Array[f, 65] (* Robert G. Wilson v, Jun 08 2010 *)

PROG

(Haskell)

a026239 1 = 1

a026239 n | a010051 n == 1 = a002808 $ a049084 n

          | otherwise      = a000040 $ a066246 n

-- Reinhard Zumkeller, Mar 30 2014

CROSSREFS

Cf. A236854.

Sequence in context: A088516 A114538 A181096 * A171547 A114579 A021220

Adjacent sequences:  A026236 A026237 A026238 * A026240 A026241 A026242

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

More terms from Robert G. Wilson v, Jun 08 2010

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 16 23:44 EST 2019. Contains 319206 sequences. (Running on oeis4.)