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Search: id:A102846
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| A102846 |
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a(0)=1, a(1)=1, a(n)=a(n-1)*a(n-2)+2. |
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+0
1
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| 1, 1, 3, 5, 17, 87, 1481, 128849, 190825371, 24587658227981, 4691949003375676905953, 115364038518117215020660724770070895, 541282185550473269502054702460138578085934426170057537937
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Prime for n=2,3,4 (a Fermat prime each time); prime for n=6. When is the next prime in the sequence? Semiprime for a(5) = 87 = 3 * 29, a(10) = 127 * 36944480341540763039. a(11) has 36 digits and is the product of 6 primes. a(12) has 57 digits and is the product of 4 primes. a(13) has 92 digits and is the product of at least 4 primes: 123419 * 35173043 * 80-digit-composite, with the second-smallest prime divisor starting with the concatenation of a(2),a(3),a(4). - Jonathan Vos Post (jvospost3(AT)gmail.com), Feb 28 2005
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EXAMPLE
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a(4)=17, a(5)=87, a(5)=17*87+2 = 1481
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MAPLE
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a[0]:=1: a[1]:=1: for n from 2 to 13 do a[n]:=a[n-1]*a[n-2]+2 od: seq(a[n], n=0..13); (Deutsch)
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CROSSREFS
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Sequence in context: A125957 A137460 A102295 this_sequence A100003 A114161 A087858
Adjacent sequences: A102843 A102844 A102845 this_sequence A102847 A102848 A102849
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KEYWORD
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easy,nonn
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AUTHOR
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Miklos Kristof (kristmikl(AT)freemail.hu), Feb 28 2005
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EXTENSIONS
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More terms from Emeric Deutsch, deutsch(AT)duke.poly.edu, Mar 08 2005
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