OFFSET
1,2
FORMULA
a(n) = (a(n-1) + a(n-4)) * (a(n-2) - a(n-3)) with a(1)=1, a(2)=2, a(3)=3 and a(4)=4
a(n) = k^(phi^n + o(1)) with k = 1.06164666362... and phi = (1+sqrt(5))/2. [Charles R Greathouse IV, Jun 21 2011]
EXAMPLE
a(5) = (4+1)*(3-2) = 5 ; a(6) = (5+2)*(4-3) = 7
MATHEMATICA
RecurrenceTable[{a[1]==1, a[2]==2, a[3]==3, a[4]==4, a[n]==(a[n-1]+ a[n-4])(a[n-2]- a[n-3])}, a, {n, 20}] (* Harvey P. Dale, Mar 08 2020 *)
PROG
(PARI) a=vector(20, i, i); for(n=6, #a, a[n]=(a[n-1]+a[n-4])*(a[n-2]-a[n-3])); a \\ Charles R Greathouse IV, Jun 21 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Karsten Meyer, Jun 18 2011
STATUS
approved