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A113790 In each block of 5 consecutive natural numbers, swap first and 2nd and swap 4th and 5th. 0
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, 26, 28, 30, 29, 32, 31, 33, 35, 34, 37, 36, 38, 40, 39, 42, 41, 43, 45, 44, 47, 46, 48, 50, 49, 52, 51, 53, 55, 54, 57, 56, 58, 60, 59, 62, 61, 63, 65, 64, 67, 66, 68, 70, 69, 72, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

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

LINKS

Table of n, a(n) for n=1..72.

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

FORMULA

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

MATHEMATICA

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

CROSSREFS

Sequence in context: A256371 A064429 A234751 * A181094 A282666 A181560

Adjacent sequences:  A113787 A113788 A113789 * A113791 A113792 A113793

KEYWORD

nonn

AUTHOR

Zak Seidov, Jan 21 2006

STATUS

approved

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Last modified October 30 05:44 EDT 2020. Contains 338077 sequences. (Running on oeis4.)