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Search: id:A072850
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| A072850 |
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Number of permutations satisfying i-2<=p(i)<=i+4, i=1..n. |
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61
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| 1, 2, 6, 18, 54, 146, 391, 1081, 3004, 8320, 22984, 63424, 175176, 484113, 1337721, 3695886, 10210702, 28209954, 77940078, 215337554, 594943087, 1643728129, 4541349672, 12547013504, 34665373744, 95774808224, 264610227072
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OFFSET
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1,2
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FORMULA
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Recurrence: a(n) = a(n - 1) + 2*a(n - 2) + 4*a(n - 3) + 6*a(n - 4) + 10*a(n - 5) + 12*a(n - 6) - 4*a(n - 7) - 6*a(n - 8) - 6*a(n - 9) - 2*a(n - 11) - 2*a(n - 12) + a(n - 14) + a(n - 15).
G.f.: - (x^9 + x^7 - 2*x^6 - 2*x^4 - 2*x^3 - x^2 + 1)/(x^15 + x^14 - 2*x^12 - 2*x^11 - 6*x^9 - 6*x^8 - 4*x^7 + 12*x^6 + 10*x^5 + 6*x^4 + 4*x^3 + 2*x^2 + x - 1)
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CROSSREFS
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Cf. A002524..A002529, A072827.
Sequence in context: A094864 A120010 A132790 this_sequence A072852 A072853 A025192
Adjacent sequences: A072847 A072848 A072849 this_sequence A072851 A072852 A072853
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KEYWORD
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nonn
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AUTHOR
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Vladimir Baltic (baltic(AT)galeb.etf.bg.ac.yu), Jul 25 2002
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