A117407 a(n) = j if n is T(j), else a(n) = k if n is U(k), where T is a Beatty sequence based on (sqrt(5)+5)/2 (A054770) and U is its complement (A063732).

1, 2, 1, 3, 4, 5, 2, 6, 7, 3, 8, 9, 10, 4, 11, 12, 13, 5, 14, 15, 6, 16, 17, 18, 7, 19, 20, 8, 21, 22, 23, 9, 24, 25, 26, 10, 27, 28, 11, 29, 30, 31, 12, 32, 33, 34, 13, 35, 36, 14, 37, 38, 39, 15, 40, 41, 16, 42, 43, 44, 17, 45, 46, 47, 18, 48, 49, 19, 50, 51, 52, 20, 53, 54, 21, 55

Offset: 0

Author

Casey Mongoven, Mar 13 2006

Keywords

• nonn

Comments

Every positive integer occurs exactly twice. Taking a Lucas number (A000032) of terms L(n) starting at a(0), the last two terms are a pair of Fibonacci numbers (A000045). If n is even, then the last two terms are F(n+1) followed by F(n-1), if n is odd they are F(n-1) followed by F(n+1), where F is the Fibonacci sequence. For example, the first L(4) = 7 terms of this sequence are (1,2,1,3,4,5,2) and the last members are 5 and 2 which are equal to F(5) and F(3). Note also that L(n) = F(n-1) + F(n+1).

Examples

			a(9) = 3 because 9 = T(3).
		

Crossrefs

Cf. A026272, A026242.