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 A131323 Odd numbers n such that the binary expansion of n ends in an even number of 1's. 22
 3, 11, 15, 19, 27, 35, 43, 47, 51, 59, 63, 67, 75, 79, 83, 91, 99, 107, 111, 115, 123, 131, 139, 143, 147, 155, 163, 171, 175, 179, 187, 191, 195, 203, 207, 211, 219, 227, 235, 239, 243, 251, 255, 259, 267, 271, 275, 283, 291, 299, 303, 307, 315, 319, 323, 331 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers of the form (4^a)*b - 1 with positive integer a and odd integer b. The sequence has linear growth and the limit of a(n)/n is 6. - Stefan Steinerberger, Dec 18 2007 Evil and odious terms alternate. - Vladimir Shevelev, Jun 22 2009 Also odd numbers of the form n=(A079523(k)-1)/2. - Vladimir Shevelev, Jul 06 2009 As a set, this is the complement of A079523 in the odd numbers. - Michel Dekking, Feb 13 2019 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 Thomas Zaslavsky, Anti-Fibonacci Numbers: A Formula, Sep 26 2016 FORMULA a(n) = 2*A079523(n) + 1. - Michel Dekking, Feb 13 2019 EXAMPLE 11 in binary is 1011, which ends with two 1's. MAPLE N:= 1000: # to get all terms up to N Odds:= [seq(2*i+1, i=0..floor((N-1)/2)]: f:= proc(n) local L, x;    L:= convert(n, base, 2);    x:= ListTools:-Search(0, L);    if x = 0 then type(nops(L), even) else type(x, odd) fi end proc: A131323:= select(f, Odds); # Robert Israel, Apr 02 2014 MATHEMATICA Select[Range[500], OddQ[ # ] && EvenQ[FactorInteger[ # + 1][[1, 2]]] &] (* Stefan Steinerberger, Dec 18 2007 *) en1Q[n_]:=Module[{ll=Last[Split[IntegerDigits[n, 2]]]}, Union[ll] =={1} &&EvenQ[Length[ll]]]; Select[Range[1, 501, 2], en1Q] (* Harvey P. Dale, May 18 2011 *) PROG (PARI) is(n)=n%2 && valuation(n+1, 2)%2==0 \\ Charles R Greathouse IV, Aug 20 2013 CROSSREFS Cf. A079523, A121539. Sequence in context: A044971 A106374 A075330 * A050592 A032466 A060698 Adjacent sequences:  A131320 A131321 A131322 * A131324 A131325 A131326 KEYWORD nonn,easy AUTHOR Nadia Heninger and N. J. A. Sloane, Dec 16 2007 EXTENSIONS More terms from Stefan Steinerberger, Dec 18 2007 STATUS approved

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Last modified April 11 16:42 EDT 2021. Contains 342888 sequences. (Running on oeis4.)