A132669 a(1)=1, a(n) = 5*a(n-1) if the minimal positive integer not yet in the sequence is greater than a(n-1), else a(n) = a(n-1) - 1.

1, 5, 4, 3, 2, 10, 9, 8, 7, 6, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 155, 154, 153, 152, 151, 150, 149, 148, 147, 146, 145, 144, 143

Offset

1,2

Comments

Also: a(1)=1, a(n) = maximal positive integer < a(n-1) not yet in the sequence, if it exists, else a(n) = 5*a(n-1).

Also: a(1)=1, a(n) = a(n-1) - 1, if a(n-1) - 1 > 0 and has not been encountered so far, else a(n) = 5*a(n-1).

A permutation of the positive integers. The sequence is self-inverse, in that a(a(n)) = n.

Links

Table of n, a(n) for n=1..68.

Formula

G.f.: g(x) = (x(1-2x)/(1-x) + 5x^2*f'(x^(9/4)) + (9/25)*(f'(x^(1/4)) - 5x - 1))/(1-x) where f(x) = Sum_{k>=0} x^(5^k) and f'(z) = derivative of f(x) at x = z.

a(n) = (14*5^(r/2) - 6)/4 - n, if both r and s are even, else a(n) = (34*5^((s-1)/2) - 6)/4 - n, where r = ceiling(2*log_5((4n+5)/9)) and s = ceiling(2*log_5((4n+5)/5)) - 1.

a(n) = (5^floor(1 + (k+1)/2) + 9*5^floor(k/2) - 6)/4 - n, where k=r, if r is odd, else k=s (with respect to r and s above; formally, k = ((r+s) - (r-s)*(-1)^r)/2).

a(n) = A133629(m) + A133629(m+1) + 1 - n, where m:=max{ k | A133629(k) < n }.

a(A133629(n) + 1) = A133629(n+1).

a(A133629(n)) = A133629(n-1) + 1 for n > 0.

Crossrefs

For formulas concerning a general parameter p (with respect to the recurrence rule ... a(n) = p*a(n-1) ...) see A132374.

For p=2 to p=10 see A132666 through A132674.

Cf. A087503.

Sequence in context: A094097 A145330 A194744 * A276052 A374420 A348340

Adjacent sequences: A132666 A132667 A132668 * A132670 A132671 A132672

Keyword

nonn

Author

Hieronymus Fischer, Sep 15 2007, Sep 23 2007

Status

approved