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 A100307 Modulo 2 binomial transform of 3^n. 7
 1, 4, 10, 40, 82, 328, 820, 3280, 6562, 26248, 65620, 262480, 538084, 2152336, 5380840, 21523360, 43046722, 172186888, 430467220, 1721868880, 3529831204, 14119324816, 35298312040, 141193248160, 282472589764, 1129890359056 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS 3^n may be retrieved through 3^n = Sum_{k=0..n} (-1)^A010060(n-k)*(binomial(n,k) mod 2)*a(k). LINKS Gheorghe Coserea, Table of n, a(n) for n = 0..200 Vladimir Shevelev, On Stephan's conjectures concerning Pascal triangle modulo 2 and their polynomial generalization, arXiv:1011.6083 [math.NT], 2010-2012; J. of Algebra Number Theory: Advances and Appl., 7 (2012), no.1, 11-29. FORMULA a(n) = Sum_{k=0..n} (binomial(n, k) mod 2)*3^k. From Vladimir Shevelev, Dec 26-27 2013: (Start) Sum_{n>=0} 1/a(n)^r = Product_{k>=0} (1 + 1/(3^(2^k)+1)^r), Sum_{n>=0} (-1)^A000120(n)/a(n)^r = Product_{k>=0} (1 - 1/(3^(2^k)+1)^r), where r > 0 is a real number. In particular, Sum_{n>=0} 1/a(n) = Product_{k>=0} (1 + 1/(3^(2^k)+1)) = 1.391980...; Sum_{n>=0} (-1)^A000120(n)/a(n) = 2/3. a(2^n) = 3^(2^n)+1, n >= 0. Note that analogs of Stephan's limit formulas (see Shevelev link) reduce to the relations: a(2^t*n+2^(t-1)) = 8*(3^(2^(t-1)+1))/(3^(2^(t-1))-1) * a(2^t*n+2^(t-1)-2), t >= 2. In particular, for t=2,3,4, we have the following formulas: a(4*n+2) = 10 * a(4*n), a(8*n+4) = (41/5) * a(8*n+2), a(16*n+8) = (3281/410) * a(16*n+6), etc. (End) From Tom Edgar, Oct 11 2015: (Start) a(n) = Product_{b_j != 0} a(2^j) where n = Sum_{j>=0} b_j*2^j is the binary representation of n. a(2*k+1) = 4*a(2*k). (End) MATHEMATICA Table[Sum[Mod[Binomial[n, k], 2]3^k, {k, 0, n}], {n, 0, 40}] (* Harvey P. Dale, Aug 28 2013 *) PROG (Sage) [sum((binomial(n, k)%2)*3^k for k in [0..n]) for n in [0..50]] # Tom Edgar, Oct 11 2015 (PARI) a(n) = subst(lift((Mod(1, 2)+'x)^n), 'x, 3); \\ Gheorghe Coserea, Jun 11 2016 (Magma) [(&+[3^k*(Binomial(n, k) mod 2): k in [0..n]]): n in [0..40]]; // G. C. Greubel, Feb 03 2023 (Python) def A100307(n): return sum((bool(~n&n-k)^1)*3**k for k in range(n+1)) # Chai Wah Wu, May 02 2023 CROSSREFS Cf. A001316, A001317, A038183, A100308, A100309, A100310, A100311. Sequence in context: A149203 A038168 A186337 * A238721 A077811 A136855 Adjacent sequences: A100304 A100305 A100306 * A100308 A100309 A100310 KEYWORD easy,nonn AUTHOR Paul Barry, Dec 06 2004 STATUS approved

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Last modified July 12 14:24 EDT 2024. Contains 374251 sequences. (Running on oeis4.)