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 A145204 Numbers whose representation in base 3 (A007089) ends in an odd number of zeros. 17
 0, 3, 6, 12, 15, 21, 24, 27, 30, 33, 39, 42, 48, 51, 54, 57, 60, 66, 69, 75, 78, 84, 87, 93, 96, 102, 105, 108, 111, 114, 120, 123, 129, 132, 135, 138, 141, 147, 150, 156, 159, 165, 168, 174, 177, 183, 186, 189, 192, 195, 201, 204, 210, 213, 216, 219, 222, 228, 231 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Previous name: Complement of A007417. Also numbers having infinitary divisor 3, or the same, having factor 3 in their Fermi-Dirac representation as product of distinct terms of A050376. - Vladimir Shevelev, Mar 18 2013 For n > 1: where even terms occur in A051064. - Reinhard Zumkeller, May 23 2013 If we exclude a(1) = 0, these are numbers whose squarefree part is divisible by 3, which can be partitioned into numbers whose squarefree part is congruent to 3 mod 9 (A055041) and 6 mod 9 (A055040) respectively. - Peter Munn, Jul 14 2020 The inclusion of 0 as a term might be viewed as a cultural preference: if we habitually wrote numbers enclosed in brackets and then used a null string of digits for zero, the natural number sequence in ternary would be [], [1], [2], [10], [11], [12], [20], ... . - Peter Munn, Aug 02 2020 The asymptotic density of this sequence is 1/4. - Amiram Eldar, Sep 20 2020 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Aviezri S. Fraenkel, The vile, dopey, evil and odious game players, Discrete Math. 312 (2012), no. 1, 42-46. FORMULA a(n) = 3 * A007417(n-1) for n > 1. A014578(a(n)) = 0. For n > 1, A007949(a(n)) mod 2 = 1. [Edited by Peter Munn, Aug 02 2020] {a(n) : n >= 2} = {A052330(A042964(k)) : k >= 1} = {A064614(A036554(k)) : k >= 1}. - Peter Munn, Aug 31 2019 and Dec 06 2020 MAPLE isA145204 := proc(n) local d, c; if n = 0 then return true fi; d := A007089(n); c := 0; while irem(d, 10) = 0 do c := c+1; d := iquo(d, 10) od; type(c, odd) end: select(isA145204, [\$(0..231)]); # Peter Luschny, Aug 05 2020 MATHEMATICA Select[ Range[0, 235], (# // IntegerDigits[#, 3]& // Split // Last // Count[#, 0]& // OddQ)&] (* Jean-François Alcover, Mar 18 2013 *) Join[{0}, Select[Range[235], OddQ @ IntegerExponent[#, 3] &]] (* Amiram Eldar, Sep 20 2020 *) PROG (Haskell) a145204 n = a145204_list !! (n-1) a145204_list = 0 : map (+ 1) (findIndices even a051064_list) -- Reinhard Zumkeller, May 23 2013 # Python import numpy as np def isA145204(n):     if n == 0: return True     c = 0     d = int(np.base_repr(n, base = 3))     while d % 10 == 0:         c += 1         d //= 10     return c % 2 == 1 print([n for n in range(231) if isA145204(n)]) # Peter Luschny, Aug 05 2020 CROSSREFS Subsequence of A008585, A028983. Subsequences: A016051, A055040, A055041, A329575. Cf. A007089, A007417 (complement), A050376, A182581 (characteristic function). Positions of 0s in A014578. Excluding 0: the positions of odd numbers in A007949; equivalently, of even numbers in A051064; symmetric difference of A003159 and A036668. Related to A042964 via A052330. Related to A036554 via A064614. Sequence in context: A319451 A256882 A191267 * A016051 A070790 A114614 Adjacent sequences:  A145201 A145202 A145203 * A145205 A145206 A145207 KEYWORD nonn AUTHOR Reinhard Zumkeller, Oct 04 2008 EXTENSIONS New name using a comment of Vladimir Shevelev by Peter Luschny, Aug 05 2020 STATUS approved

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Last modified August 5 21:45 EDT 2021. Contains 346488 sequences. (Running on oeis4.)