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Search: id:A072688
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| A072688 |
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Of the first n integers (inclusive), how many of them have a prime number of letters in their English names? |
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+0
1
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| 1, 2, 3, 3, 3, 4, 5, 6, 6, 7, 7, 7, 7, 7, 8, 9, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 12, 13, 13, 13, 13, 13, 14, 14, 14, 14, 15, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 20
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(n)=number of terms of A072685 <= n.
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EXAMPLE
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Sequence A072685 begins: 1, 2, 3, 6, 7, 8, 10 so there are 3 terms up to and including n=4, 3 terms up to and including n=5, 6 terms up to and including n=9. Therefore a(4)=3, a(5)=3, a(9)=6.
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CROSSREFS
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Cf. A072685, A072687.
Sequence in context: A051134 A037458 A064474 this_sequence A120504 A025772 A029069
Adjacent sequences: A072685 A072686 A072687 this_sequence A072689 A072690 A072691
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KEYWORD
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easy,nonn,word
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AUTHOR
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Mark Hudson (mrmarkhudson(AT)hotmail.com), Jul 02 2002
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