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A338692
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Positions of 1's in A209615.
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6
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1, 4, 5, 6, 9, 13, 14, 16, 17, 20, 21, 22, 24, 25, 29, 30, 33, 36, 37, 38, 41, 45, 46, 49, 52, 53, 54, 56, 57, 61, 62, 64, 65, 68, 69, 70, 73, 77, 78, 80, 81, 84, 85, 86, 88, 89, 93, 94, 96, 97, 100, 101, 102, 105, 109, 110, 113, 116, 117, 118, 120, 121, 125, 126
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OFFSET
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1,2
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COMMENTS
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Also positions of 1's and 4's in A003324.
Numbers of the form (2*k+1) * 2^e where k+e is even. In other words, union of {(4*m+1) * 2^(2t)} and {(4*m+3) * 2^(2t+1)}, where m >= 0, t >= 0.
Numbers whose quaternary (base-4) expansion ends in 100...00 or 1200..00 or 3200..00. Trailing 0's are not necessary.
There are precisely 2^(N-1) terms <= 2^N for every N >= 1.
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LINKS
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FORMULA
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EXAMPLE
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14 is a term since it is in the family {(4*m+3) * 2^(2t+1)} with m = 1, t = 0.
16 is a term since it is in the family {(4*m+1) * 2^(2t)} with m = 0, t = 2.
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PROG
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(PARI) isA338692(n) = my(e=valuation(n, 2), k=bittest(n, e+1)); !((k+e)%2)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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