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A078918
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a(n) = (a(n-1) + a(n-3)) * a(n-2) / a(n-4). a(1) = a(2) = a(3) = a(4) = 1.
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2
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1, 1, 1, 1, 2, 3, 8, 30, 132, 1400, 23595, 1107260, 198172975, 156753667213, 1316573850509365, 186386043285609148267, 1238266675343181339894414632, 1472345944138437490816316070884292123
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OFFSET
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1,5
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LINKS
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FORMULA
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a(n) * a(n-6) = (a(n-1) + a(n-3)) * (a(n-3) + a(n-5)) for all n in Z. - Michael Somos, Dec 25 2013
a(n) = 6 * a(n-2) * a(n-3) - (a(n-2) + a(n-3) + a(n-5)) for all n in Z. - Michael Somos, May 30 2022
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MATHEMATICA
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a[ n_] := a[n] = If[n < 1, a[5 - n], If[n < 5, 1, (a[n - 1] + a[n - 3]) a[n - 2] / a[n - 4]]]; (* Michael Somos, Dec 25 2013 *)
a[ n_] := a[n] = If[n < 1, a[5 - n], If[n < 6, Max[1, n - 3], 6*a[n - 2]*a[n-3] - (a[n - 2] + a[n - 3] + a[n - 5])]]; (* Michael Somos, May 30 2022 *)
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PROG
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(PARI) {a(n) = if( n<1, n = 5-n); if( n<5, 1, (a(n-1) + a(n-3)) * a(n-2) / a(n-4))}; /* Michael Somos, Dec 25 2013 */
(PARI) {a(n) = if( n<1, n = 5-n); if( n<6, max(1, n-3), 6*a(n-2)*a(n-3) - (a(n-2)+a(n-3)+a(n-5)))}; /* Michael Somos, May 30 2022 */
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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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