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 A334841 a(0) = 0; for n > 0, a(n) = (number of 1's and 3's in base 4 representation of n) - (number of 0's and 2's in base 4 representation of n). 2
 0, 1, -1, 1, 0, 2, 0, 2, -2, 0, -2, 0, 0, 2, 0, 2, -1, 1, -1, 1, 1, 3, 1, 3, -1, 1, -1, 1, 1, 3, 1, 3, -3, -1, -3, -1, -1, 1, -1, 1, -3, -1, -3, -1, -1, 1, -1, 1, -1, 1, -1, 1, 1, 3, 1, 3, -1, 1, -1, 1, 1, 3, 1, 3, -2, 0, -2, 0, 0, 2, 0, 2, -2, 0, -2, 0, 0, 2, 0, 2, 0, 2, 0, 2, 2, 4, 2, 4, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 COMMENTS Values are even for base 4 representations of n with an even number of digits, and odd for base 4 representations of n with an odd number of digits, except for a(0). LINKS FORMULA a(n) = 2*A139351(n) - A110592(n), n>0. - R. J. Mathar, Sep 02 2020 EXAMPLE n in    #odd    #even   n  base 4  digits - digits = a(n)   =  ======  =======================   0    0        0   -            0   1    1        1   -    0   =   1   2    2        0   -    1   =  -1   3    3        1   -    0   =   1   4   10        1   -    1   =   0   5   11        2   -    0   =   2   6   12        1   -    1   =   0   7   13        2   -    0   =   2 MAPLE a:= n-> `if`(n=0, 0, add(`if`(i in [1, 3], 1, -1), i=convert(n, base, 4))): seq(a(n), n=0..100);  # Alois P. Heinz, May 30 2020 MATHEMATICA a[0] = 0; a[n_] := Total[-(-1)^(r = Range[0, 3]) * DigitCount[n, 4, r]]; Array[a, 100, 0] (* Amiram Eldar, May 13 2020 *) Join[{0}, Table[Total[If[EvenQ[#], -1, 1]&/@IntegerDigits[n, 4]], {n, 90}]] (* Harvey P. Dale, Sep 06 2020 *) PROG (R) qnary = function(n, e, q){   e = floor(n/4)   q = n%%4   if(n == 0 ){return(0)}   if(e == 0){return(q)}   else{return(c(qnary(e), (q)))} } m = 400 s = seq(2, m) v = c(0) for(i in s){   x = qnary(i-1)   x[which(x%%2!=0)] = 1   x[which(x%%2==0)] = -1   v[i] = sum(x) } (Python) import numpy as np def qnary(n):     e = n//4     q = n%4     if n == 0 : return 0     if e == 0 : return q     if e != 0 : return np.append(qnary(e), q) m = 400 v = [0] for i in range(1, m+1) :     t = np.array(qnary(i))     t[t%2 != 0] = 1     t[t%2 == 0] = -1     v = np.append(v, np.sum(t)) (PARI) a(n) = my(ret=0); if(n, forstep(i=0, logint(n, 2), 2, if(bittest(n, i), ret++, ret--))); ret; \\ Kevin Ryde, May 24 2020 (Python) def A334841(n):     return 2*bin(n)[-1:1:-2].count('1')-(len(bin(n))-1)//2 if n > 0 else 0 # Chai Wah Wu, Sep 03 2020 CROSSREFS Cf. A053737, A010065, A037863, A007090, A301336, A333596. Sequence in context: A106277 A088627 A230205 * A024713 A123530 A161516 Adjacent sequences:  A334838 A334839 A334840 * A334842 A334843 A334844 KEYWORD sign,easy,base AUTHOR Alexander Van Plantinga, May 13 2020 STATUS approved

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Last modified July 27 02:39 EDT 2021. Contains 346302 sequences. (Running on oeis4.)