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A338691
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Positions of (-1)'s in A209615.
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6
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2, 3, 7, 8, 10, 11, 12, 15, 18, 19, 23, 26, 27, 28, 31, 32, 34, 35, 39, 40, 42, 43, 44, 47, 48, 50, 51, 55, 58, 59, 60, 63, 66, 67, 71, 72, 74, 75, 76, 79, 82, 83, 87, 90, 91, 92, 95, 98, 99, 103, 104, 106, 107, 108, 111, 112, 114, 115, 119, 122, 123, 124, 127, 128
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OFFSET
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1,1
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COMMENTS
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Also positions of 2's and 3's in A003324.
Numbers of the form (2*k+1) * 2^e where k+e is odd. In other words, union of {(4*m+1) * 2^(2t+1)} and {(4*m+3) * 2^(2t)}, where m >= 0, t >= 0.
Numbers whose quaternary (base-4) expansion ends in 300...00 or 0200..00 or 2200..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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15 is a term since it is in the family {(4*m+3) * 2^(2t)} with m = 3, t = 0.
18 is a term since it is in the family {(4*m+1) * 2^(2t+1)} with m = 2, t = 0.
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PROG
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(PARI) isA338691(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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