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A360296
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a(1) = 1, and for any n > 1, a(n) is the sum of the terms of the sequence at indices k < n whose binary digits appear in order but not necessarily as consecutive digits in the binary representation of n.
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1
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1, 1, 1, 2, 3, 3, 2, 4, 8, 11, 8, 8, 11, 8, 4, 8, 20, 34, 26, 34, 51, 40, 20, 20, 40, 51, 34, 26, 34, 20, 8, 16, 48, 96, 76, 118, 186, 152, 76, 96, 208, 281, 186, 152, 208, 124, 48, 48, 124, 208, 152, 186, 281, 208, 96, 76, 152, 186, 118, 76, 96, 48, 16, 32
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OFFSET
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1,4
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COMMENTS
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This sequence is a variant of A165418.
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LINKS
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FORMULA
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a(2^k) = 2^(k-1) for any k > 0.
a(2^k-1) = 2^(k-2) for any k > 1.
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EXAMPLE
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The first terms, alongside the corresponding k's, are:
n a(n) k's
-- ---- ------------------
1 1 N/A
2 1 {1}
3 1 {1}
4 2 {1, 2}
5 3 {1, 2, 3}
6 3 {1, 2, 3}
7 2 {1, 3}
8 4 {1, 2, 4}
9 8 {1, 2, 3, 4, 5}
10 11 {1, 2, 3, 4, 5, 6}
11 8 {1, 2, 3, 5, 7}
12 8 {1, 2, 3, 4, 6}
13 11 {1, 2, 3, 5, 6, 7}
14 8 {1, 2, 3, 6, 7}
15 4 {1, 3, 7}
16 8 {1, 2, 4, 8}
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PROG
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(PARI) { for (n=1, #a=vector(64), print1 (a[n]=if (n==1, 1, s = [1]; b = binary(n); for (k=2, #b, s = setunion(s, apply(v -> 2*v+b[k], s))); sum(k=1, #s-1, a[s[k]]); )", ")) }
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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