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A072688 Of the first n integers (inclusive), how many of them have a prime number of letters in their English names? 0

%I

%S 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,

%T 13,13,13,13,14,14,14,14,15,16,16,17,17,17,17,17,17,17,17,17,17,18,18,

%U 18,18,18,18,18,18,18,18,19,19,19,19,19,19,19,19,19,19,20

%N Of the first n integers (inclusive), how many of them have a prime number of letters in their English names?

%F a(n)=number of terms of A072685 <= n.

%e 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.

%Y Cf. A072685, A072687.

%K easy,nonn,word

%O 1,2

%A Mark Hudson (mrmarkhudson(AT)hotmail.com), Jul 02 2002

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