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A020330 Numbers n such that base 2 representation is the juxtaposition of two identical strings. 9
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 June 25 19:53 EDT 2017. Contains 288729 sequences.