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A020330 Numbers n such that base 2 representation is the juxtaposition of two identical strings. 11
3, 10, 15, 36, 45, 54, 63, 136, 153, 170, 187, 204, 221, 238, 255, 528, 561, 594, 627, 660, 693, 726, 759, 792, 825, 858, 891, 924, 957, 990, 1023, 2080, 2145, 2210, 2275, 2340, 2405, 2470, 2535, 2600, 2665, 2730, 2795, 2860, 2925, 2990, 3055, 3120, 3185, 3250 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All differences are in union of A000051 and A001576. - Vladimir Shevelev, Dec 07 2013

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..8191

FORMULA

a(n) = n + 2n*2^floor(log2(n)). - Ralf Stephan, Dec 07 2004

EXAMPLE

36 is a member because 36 = 100100_2 which is 100 followed by 100.

MATHEMATICA

Table[n + 2 n*2^Floor[Log[2, n]], {n, 50}] (* T. D. Noe, Dec 10 2013 *)

PROG

(Haskell)

a020330 n = foldr (\d v -> 2 * v + d) 0 (bs ++ bs) where

   bs = a030308_row n

-- Reinhard Zumkeller, Feb 19 2013

(PARI) a(n)=n+n<<#binary(n) \\ Charles R Greathouse IV, Mar 29 2013

(PARI) is(n)=my(L=#binary(n)\2); n>>L==bitand(n, 2^L-1) \\ Charles R Greathouse IV, Mar 29 2013

CROSSREFS

Subsequence of A121016.

Cf. A062383, A030308, A007088.

Column k=0 of A246830, column k=1 of A246834.

Sequence in context: A129307 A186575 A233312 * A023861 A037345 A217278

Adjacent sequences:  A020327 A020328 A020329 * A020331 A020332 A020333

KEYWORD

nonn,base,easy,look

AUTHOR

David W. Wilson, Melia Aldridge, ma38(AT)spruce.evansville.edu

STATUS

approved

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Last modified August 20 03:34 EDT 2017. Contains 290823 sequences.