A213912 a(1) = 1; for n>1, a(n) = floor(sqrt(a(n-1))) if that number is not already in the sequence, otherwise a(n) = 3*a(n-1).

1, 3, 9, 27, 5, 2, 6, 18, 4, 12, 36, 108, 10, 30, 90, 270, 16, 48, 144, 432, 20, 60, 7, 21, 63, 189, 13, 39, 117, 351, 1053, 32, 96, 288, 864, 29, 87, 261, 783, 2349, 7047, 83, 249, 15, 45, 135, 11, 33, 99, 297, 17, 51, 153, 459, 1377, 37, 111, 333, 999, 31

Offset: 1

Author

Reinhard Zumkeller, Mar 05 2013

Keywords

• nonn
• look

Comments

Permutation of natural numbers with inverse A213913.

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Index entries for sequences that are permutations of the natural numbers

Crossrefs

Cf. A114183.

Programs

Haskell

a213912 n = a213912_list !! (n-1)
a213912_list = 1 : f [1] where
   f xs@(x:_) = y : f (y : xs) where
     y = if z `notElem` xs then z else 3 * x where z = a000196 x

PARI

lista(nn) = {my(k, v=vector(nn)); v[1]=1; for(n=2, nn, if(vecsearch(vecsort(v), k=sqrtint(v[n-1])), v[n]=3*v[n-1], v[n]=k)); v; } \\ Jinyuan Wang, Jun 26 2020