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 A047778 Concatenation of first n numbers in binary, converted to base 10. 28
 1, 6, 27, 220, 1765, 14126, 113015, 1808248, 28931977, 462911642, 7406586283, 118505380540, 1896086088653, 30337377418462, 485398038695407, 15532737238253040, 497047591624097297, 15905522931971113522 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The smallest prime in this sequence is 485398038695407. What is the full subsequence of primes? - N. J. A. Sloane, Oct 03 2015 There is only the one prime in the first 22400 terms, making a second prime > 10^91000. - Hans Havermann, Oct 07 2015 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..250 FORMULA a(n) = a(n-1)*2^(1+floor(log_2(n))) + n. - Henry Bottomley, Jan 12 2001 a(n) = 4C / 2^frac(log_2(n)) * n^{n+1} / r(frac(log_2(n)))^n + O(1), where r(x) = 2^{x - 1 + 2^{1-x}}; frac is the fractional part function frac(x) = x - floor(x); and C is the binary Champernowne constant (A066716). (In fact, a(n) is the floor of this expression; the error term is between 1/2 and 1.) r(x) takes on values between e*log(2) and 2 for x in the range 0 to 1. It follows using Stirling's approximation that the radius of convergence for the e.g.f. is log 2. - Franklin T. Adams-Watters, Sep 07 2006 EXAMPLE a(4) = 1 10 11 100 [base 2] = 220 [base 10]. MAPLE conc:= (x, y) -> x*2^(1+ilog2(y))+y: a:= 1: for n from 2 to 30 do a[n]:= conc(a[n-1], n) od: seq(a[n], n=1..30); # Robert Israel, Oct 07 2015 MATHEMATICA If[STARTPOINT==1, n={}, n=Flatten[IntegerDigits[Range[STARTPOINT-1], 2]]]; Table[AppendTo[n, IntegerDigits[w, 2]]; n=Flatten[n]; FromDigits[n, 2], {w, STARTPOINT, ENDPOINT}] (* Dylan Hamilton, Aug 04 2010 *) f[n_] := FromDigits[ Flatten@ IntegerDigits[ Range@n, 2], 2]; Array[f, 18] (* Robert G. Wilson v, Nov 07 2010 *) PROG (Haskell) a047778 = (foldl (\v d -> 2*v + d) 0) . concatMap (reverse . unfoldr    (\x -> if x == 0 then Nothing else Just \$ swap \$ divMod x 2)) .    enumFromTo 1 -- Reinhard Zumkeller, Feb 19 2012 (PARI) cb(a, b)=a<<#binary(b) + b a(n)=fold(cb, [1..n]) \\ Charles R Greathouse IV, Jun 21 2017 (PARI) A047778_vec(N=20, s)=vector(N, k, s=s<

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Last modified February 20 17:04 EST 2020. Contains 332080 sequences. (Running on oeis4.)