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Search: id:A100681
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| A100681 |
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Inverse modulo 2 modulo transform of 10^n. |
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+0
1
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| 1, 9, 99, 891, 9999, 89991, 989901, 8909109, 99999999, 899999991, 9899999901, 89099999109, 999899990001, 8999099910009, 98990099010099, 890910891090891, 9999999999999999, 89999999999999991, 989999999999999901
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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10^n may be retrieved as sum{k=0..n, mod(binomial(n,k),2)A100743(k)}.
These can never be prime nor (after 9) semiprime, as easily seen from sum-of-digits, equivalently divisibility by powers of 3. - Jonathan Vos Post (jvospost2(AT)yahoo.com), Dec 07 2004
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FORMULA
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a(n)=sum{k=0..n, (-1)^A010060(n-k)*mod(binomial(n, k), 2)10^k}.
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CROSSREFS
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Adjacent sequences: A100678 A100679 A100680 this_sequence A100682 A100683 A100684
Sequence in context: A139280 A116274 A116286 this_sequence A043044 A069000 A101564
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Dec 06 2004
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