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a(n) = floor(X/Y) where X = concatenation in decreasing order of (2n)-th even number to (n+1)-th even number and Y = that of first n even numbers in increasing order.
12

%I #8 Mar 11 2019 12:18:34

%S 2,3,49,6540,8176,9814,11451,13088,14725,16362,17999,19636,21273,

%T 22910,24547,26184,27821,29458,31095,32732,34369,36006,37643,39280,

%U 40917,4217902,438013252,45423626657,4704592803725,486682294165577

%N a(n) = floor(X/Y) where X = concatenation in decreasing order of (2n)-th even number to (n+1)-th even number and Y = that of first n even numbers in increasing order.

%H Harvey P. Dale, <a href="/A067092/b067092.txt">Table of n, a(n) for n = 0..1000</a>

%e a(3) = floor[12108/246] = 49. a(8) = floor [ 3230282624222018/246810121416] = floor[13088.128662184629278356029087656] = 13088.

%t Table[Floor[FromDigits[Flatten[IntegerDigits/@Range[4n,2n+2,-2]]]/ FromDigits[ Flatten[IntegerDigits/@Range[2,2n,2]]]],{n,30}] (* _Harvey P. Dale_, Mar 11 2019 *)

%Y Cf. A067088, A067089, A067090, A067091.

%K easy,nonn,base

%O 0,1

%A _Amarnath Murthy_, Jan 07 2002

%E More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 01 2003

%E Edited by _Charles R Greathouse IV_, Apr 23 2010