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Search: id:A113790
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| A113790 |
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In each block of 5 consecutive natural numbers, swap first and 2nd, and swap 4th and 5th. |
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+0
1
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| 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; listen)
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OFFSET
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1,1
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COMMENT
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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 R. Janjic (agnus(AT)blic.net), Apr 17 2007
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LINKS
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Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
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FORMULA
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a(n)=m+(1/2)*(n-m)(5-(n-m)^2); m=3+5*floor((n-1)/5); n=1, 2, ...
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MATHEMATICA
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m:=3+5*Floor[(n-1)/5]; Table[m+(1/2)*(n-m)*(5-(n-m)^2), {n, 1, 80}]
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CROSSREFS
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Sequence in context: A069931 A056943 A064429 this_sequence A063705 A137655 A058202
Adjacent sequences: A113787 A113788 A113789 this_sequence A113791 A113792 A113793
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Jan 21 2006
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