

A003160


a(1) = a(2) = 1, a(n) = n  a(a(n1))  a(a(n2)).
(Formerly M0446)


7



1, 1, 1, 2, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 8, 9, 9, 9, 10, 11, 12, 12, 12, 13, 14, 15, 15, 15, 16, 16, 16, 17, 17, 17, 18, 19, 20, 20, 20, 21, 21, 21, 22, 22, 22, 23, 24, 25, 25, 25, 26, 26, 26, 27, 27, 27, 28, 29, 30, 30, 30, 31, 32, 33, 33, 33, 34, 35, 36, 36, 36, 37, 37, 37, 38
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OFFSET

1,4


COMMENTS

Sequence of indices n where a(n1) < a(n) appears to be given by A003156.  Joerg Arndt, May 11 2010


REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS



FORMULA

a(n) is asymptotic to n/2.


MATHEMATICA

Block[{a = {1, 1}}, Do[AppendTo[a, i  a[[ a[[1]] ]]  a[[ a[[2]] ]] ], {i, 3, 76}]; a] (* Michael De Vlieger, Dec 31 2020 *)


PROG

(PARI) a(n)=if(n<3, 1, na(a(n1))a(a(n2)))
(Haskell)
a003160 n = a003160_list !! (n1)
a003160_list = 1 : 1 : zipWith () [3..] (zipWith (+) xs $ tail xs)
where xs = map a003160 a003160_list
(SageMath)
@CachedFunction
def a(n): return 1 if (n<3) else n  a(a(n1))  a(a(n2))


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



