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 A038713 a(n) = n XOR (n-1), i.e., nim-sum of sequential pairs, written in binary. 3
 1, 11, 1, 111, 1, 11, 1, 1111, 1, 11, 1, 111, 1, 11, 1, 11111, 1, 11, 1, 111, 1, 11, 1, 1111, 1, 11, 1, 111, 1, 11, 1, 111111, 1, 11, 1, 111, 1, 11, 1, 1111, 1, 11, 1, 111, 1, 11, 1, 11111, 1, 11, 1, 111, 1, 11, 1, 1111, 1, 11, 1, 111, 1, 11, 1, 1111111, 1, 11, 1, 111, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = (10^A001511(n) - 1)/(10 - 1). Multiplicative with a(2^e) = (10^(e+1) - 1)/9, a(p^e)=1 if p odd. Multiplicative with a(p^e) = (10^e - 1)/9 if p = 2, 1 otherwise. G.f.: Sum_{k>=0} 10^k * x^(2^k) / (1 - x^(2^k)). - Ilya Gutkovskiy, Dec 15 2020 EXAMPLE a(6) = 11 because 110 XOR 101 = 11 base 2. MATHEMATICA Table[(10^IntegerExponent[2*n, 2] - 1)/9, {n, 100}] (* Vincenzo Librandi, Mar 11 2013 *) PROG (PARI) a(n)=if(n<1, 0, (10^(valuation(n, 2)+1)-1)/9) /* Michael Somos, Apr 28 2005 */ (MAGMA) [(10^(Valuation(n, 2)+1)-1)/9: n in [1..70]]; // Vincenzo Librandi, Mar 11 2013 CROSSREFS Cf. A038712 translated to binary, A001511 translated to unary (repeated 1's). Sequence in context: A289092 A104490 A164851 * A130556 A277932 A290676 Adjacent sequences:  A038710 A038711 A038712 * A038714 A038715 A038716 KEYWORD mult,easy,nonn AUTHOR Henry Bottomley, May 02 2000 STATUS approved

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Last modified September 24 12:17 EDT 2021. Contains 347642 sequences. (Running on oeis4.)