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Search: id:A141267
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| A141267 |
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Concatenate first n double factorials in reverse order. |
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+0
3
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| 1, 21, 321, 8321, 158321, 48158321, 10548158321, 38410548158321, 94538410548158321, 384094538410548158321, 10395384094538410548158321, 4608010395384094538410548158321, 1351354608010395384094538410548158321
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Suggested by Smarandache's Concatenated Sequences.
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FORMULA
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a(n)=n!!*10^floor{1+log10[a(n-1)]}+a(n-1), with a(1)=1
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MAPLE
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P:=proc(i) local a, j, k, n; a:=1; print(1); for n from 2 by 1 to i do k:=n; j:=n-2; while j>0 do k:=k*j; j:=j-2; od; a:=k*10^floor(evalf(1+log10(a), 1000))+a; print(a); od; end: P(20);
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CROSSREFS
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Cf. A045508, A141265, A141266.
Sequence in context: A060554 A057610 A036737 this_sequence A016262 A001233 A145148
Adjacent sequences: A141264 A141265 A141266 this_sequence A141268 A141269 A141270
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KEYWORD
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nonn,base
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AUTHOR
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Paolo P. Lava (ppl(AT)spl.at), Jun 20 2008
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