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%I #10 Jul 11 2015 11:10:15
%S 1,1,1,1,1,1,3,5,9,17,65,385,3841,69087,4559417,1759931497,
%T 6761656746177,467149341275385921,2129929115299135769778433,
%U 3748529338522222733404780820902657,25346268690064943238497951432386776919871664547
%N a(n-1)*a(n-4) + a(n-2)*a(n-5) + a(n-3)*a(n-6), with a(k<6) = 1.
%C This is the 3-term analog of the 2-term recurrence A111288 a(1) = a(2) = a(3) = a(4) = 1. For n>= 5, a(n) = a(n-1)*a(n-3) + a(n-2)*a(n-4). Primes in this sequence include a(n) for n = 6, 7, 9, ... with a(21) and a(22) composite and the sequence growing beyond my ability to efficiently test primality.
%F a(0) = a(1) = a(2) = a(3) = a(4) = a(5) = 1; for n>5: a(n) = a(n-1)*a(n-4) + a(n-2)*a(n-5) + a(n-3)*a(n-6).
%t RecurrenceTable[{a[0]==a[1]==a[2]==a[3]==a[4]==a[5]==1,a[n]== a[n-1] a[n-4]+ a[n-2]a[n-5]+a[n-3]a[n-6]},a,{n,30}] (* _Harvey P. Dale_, Oct 30 2013 *)
%Y Cf. A111288, A111388.
%K easy,nonn
%O 0,7
%A _Jonathan Vos Post_, May 14 2006
%E One additional term (a(20)) from _Harvey P. Dale_, Oct 30 2013
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