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 A111235 a(1)=a(2)=a(3)=a(4)=1. For n >= 5, a(n)= a(n-1)*a(n-2) + a(n-3)*a(n-4). 2
 1, 1, 1, 1, 2, 3, 7, 23, 167, 3862, 645115, 2491437971, 1607264007306619, 4004398577225334507664179, 6436125704084114770053956998574742562466, 25772812612277833490303309040566300172816894832780792086674335463 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS a(5*n) is always even. Every other term of the sequence is odd. It is easy to see that a(n) >= A000301(n-3) for all n. From that we can deduce that a(n) >= 2^(Fibonacci(n-3)). Can anybody give a formula for the asymptotic behavior? - Stefan Steinerberger, Jan 21 2006 As n->infinity, log(a(n))/phi^n approaches t-(-1)^n*u/phi^(2*n), where phi=(1+sqrt(5))/2, t=0.0672009781433377128..., and u=0.766475715574332057.... - Jon E. Schoenfield, Sep 14 2013 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..21 MAPLE a:= proc(n) a(n):= `if`(n<5, 1, a(n-1)*a(n-2) +a(n-3)*a(n-4)) end: seq(a(n), n=1..16);  # Alois P. Heinz, Mar 30 2014 MATHEMATICA RecurrenceTable[{a[1]==a[2]==a[3]==a[4]==1, a[n]==a[n-1]a[n-2]+a[n-3] a[n-4]}, a, {n, 20}] (* Harvey P. Dale, Jun 06 2017 *) PROG (MAGMA) I:=[1, 1, 1, 1]; [n le 4 select I[n] else Self(n-1)*Self(n-2) +Self(n-3)*Self(n-4): n in [1..16]]; // Vincenzo Librandi, Mar 30 2014 CROSSREFS Cf. A239967. Sequence in context: A090253 A001064 A108176 * A066356 A006892 A296397 Adjacent sequences:  A111232 A111233 A111234 * A111236 A111237 A111238 KEYWORD easy,nonn AUTHOR Leroy Quet, Oct 28 2005 EXTENSIONS More terms from Stefan Steinerberger, Jan 21 2006 More terms from Joshua Zucker, May 04 2006 STATUS approved

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Last modified September 20 01:20 EDT 2020. Contains 337235 sequences. (Running on oeis4.)