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A276257 a(1) = a(2) = a(3) = a(4) = 1; for n>4, a(n) = ( a(n-1)+a(n-2)+a(n-3)+1 )^2 / a(n-4). 1

%I

%S 1,1,1,1,16,361,143641,20741472361,26888415586959536281,

%T 2002733778095476250641191709976062096,

%U 27923382501685315585533445603599269911720565853675615809277429923281

%N a(1) = a(2) = a(3) = a(4) = 1; for n>4, a(n) = ( a(n-1)+a(n-2)+a(n-3)+1 )^2 / a(n-4).

%C All terms are perfect squares.

%C The next term (a(12)) has 125 digits. - _Harvey P. Dale_, Jul 04 2019

%H Seiichi Manyama, <a href="/A276257/b276257.txt">Table of n, a(n) for n = 1..15</a>

%F a(n) = A276259(n)^2

%F a(n) = 25*a(n-1)*a(n-2)*a(n-3) - 2*a(n-1) - 2*a(n-2) - 2*a(n-3) - 2 - a(n-4).

%F a(n)*a(n-1)*a(n-2)*a(n-3) = ((a(n) + a(n-1) + a(n-2) + a(n-3) + 1)/5)^2.

%t RecurrenceTable[{a[1]==a[2]==a[3]==a[4]==1,a[n]==(a[n-1]+a[n-2]+ a[n-3]+ 1)^2/a[n-4]},a,{n,11}] (* _Harvey P. Dale_, Jul 04 2019 *)

%Y Cf. A276097, A276256, A276259.

%K nonn

%O 1,5

%A _Seiichi Manyama_, Aug 25 2016

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Last modified March 28 20:44 EDT 2020. Contains 333103 sequences. (Running on oeis4.)