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A276257
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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).
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1
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1, 1, 1, 1, 16, 361, 143641, 20741472361, 26888415586959536281, 2002733778095476250641191709976062096, 27923382501685315585533445603599269911720565853675615809277429923281
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OFFSET
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1,5
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COMMENTS
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All terms are perfect squares.
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LINKS
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FORMULA
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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).
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.
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MATHEMATICA
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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 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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