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Search: id:A126644
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| A126644 |
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a(n) is the number of integers k less than 10^n such that the decimal representation of k lacks the digits 1,2,3,4,5,6 and at least one of digits 7,8,9. |
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+0
3
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| 4, 16, 58, 196, 634, 1996, 6178, 18916, 57514, 174076, 525298, 1582036, 4758394, 14299756, 42948418, 128943556, 387027274, 1161475036, 3485211538, 10457207476, 31374768154, 94130595916, 282404370658, 847238277796
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Let P(A) be the power set of an n-element set A and R be a relation on P(A) such that for all x, y of P(A), xRy if either 0) x is a proper subset of y or y is a proper subset of x, 1) x is not a subset of y and y is not a subset of x and x and y are disjoint, or 2) x equals y. Then a(n) = |R|. [From Ross La Haye (rlahaye(AT)new.rr.com), Mar 19 2009]
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REFERENCES
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Ross La Haye, Binary Relations on the Power Set of an n-Element Set, Journal of Integer Sequences, Vol. 12 (2009), Article 09.2.6. [From Ross La Haye (rlahaye(AT)new.rr.com), Mar 19 2009]
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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)=3*3^n-3*2^n+1
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EXAMPLE
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a(8)=18916
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MAPLE
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f:=n->3*3^n-3*2^n+1;
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CROSSREFS
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Cf. A125630, A125948, A125947, A125946, A125945, A125940, A125909, A125908, A125880, A125897, A125904, A125858.
Sequence in context: A006079 A122032 A034514 this_sequence A092688 A123889 A123893
Adjacent sequences: A126641 A126642 A126643 this_sequence A126645 A126646 A126647
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KEYWORD
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nonn,base
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AUTHOR
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Aleksandar M. Janjic and Milan R. Janjic (agnus(AT)blic.net), Feb 08 2007
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