The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.



Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A113790 In each block of 5 consecutive natural numbers, swap first and 2nd and swap 4th and 5th. 0


%S 2,1,3,5,4,7,6,8,10,9,12,11,13,15,14,17,16,18,20,19,22,21,23,25,24,27,

%T 26,28,30,29,32,31,33,35,34,37,36,38,40,39,42,41,43,45,44,47,46,48,50,

%U 49,52,51,53,55,54,57,56,58,60,59,62,61,63,65,64,67,66,68,70,69,72,71

%N In each block of 5 consecutive natural numbers, swap first and 2nd and swap 4th and 5th.

%C Permutation of natural numbers. Or five arithmetic progressions interlaced with b(1)=2,1,3,5,4 and d=b(n+1)-b(n)=5

%C For n>=1, a(n) is equal to the number of functions f:{1,2,3}->{1,2,...,n+1} such that for fixed different x_1, x_2 in {1,2,3} and fixed y_1, y_2 in {1,2,...,n+1} we have f(x_1)<>y_1 and f(x_2)<>y_2. - _Milan Janjic_, Apr 17 2007

%H Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas for Some Functions on Finite Sets</a>

%F a(n)=m+(1/2)*(n-m)(5-(n-m)^2); m=3+5*floor((n-1)/5); n=1, 2, ...

%t m:=3+5*Floor[(n-1)/5]; Table[m+(1/2)*(n-m)*(5-(n-m)^2), {n, 1, 80}]

%K nonn

%O 1,1

%A _Zak Seidov_, Jan 21 2006

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 December 5 09:03 EST 2020. Contains 338944 sequences. (Running on oeis4.)