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A025620 Numbers of form 4^i*9^j, with i, j >= 0. 4
1, 4, 9, 16, 36, 64, 81, 144, 256, 324, 576, 729, 1024, 1296, 2304, 2916, 4096, 5184, 6561, 9216, 11664, 16384, 20736, 26244, 36864, 46656, 59049, 65536, 82944, 104976, 147456, 186624, 236196, 262144, 331776, 419904, 531441, 589824, 746496, 944784 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers of form 2^(2*i)*3^(2*j)) or 3-smooth squares: intersection of A003586 and A000290; A001221(a(n)) <= 2; A001222(a(n)) is even; A006530(a(n)) <= 3. - Reinhard Zumkeller, May 16 2015

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

PROG

(Haskell)

import Data.Set (singleton, deleteFindMin, insert)

a025620 n = a025620_list !! (n-1)

a025620_list = f $ singleton 1 where

   f s = y : f (insert (4 * y) $ insert (9 * y) s')

               where (y, s') = deleteFindMin s

-- Reinhard Zumkeller, May 16 2015

(PARI) list(lim)=my(v=List(), N); for(n=0, logint(lim\=1, 9), N=9^n; while(N<=lim, listput(v, N); N<<=2)); Set(v) \\ Charles R Greathouse IV, Jan 10 2018

CROSSREFS

Cf. A003586, A000290, A001221, A001222, A006530, subsequence of A036667.

Sequence in context: A000548 A256944 A106575 * A117218 A226076 A272711

Adjacent sequences:  A025617 A025618 A025619 * A025621 A025622 A025623

KEYWORD

easy,nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified December 5 22:37 EST 2019. Contains 329782 sequences. (Running on oeis4.)