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Search: id:A135953
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| A135953 |
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(Nonprime Fibonacci numbers with prime indices) which have exactly 2 prime factors. |
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+0
9
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| 4181, 1346269, 165580141, 53316291173, 956722026041, 2504730781961, 308061521170129, 806515533049393, 14472334024676221, 1779979416004714189, 573147844013817084101, 10284720757613717413913, 26925748508234281076009
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OFFSET
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1,1
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COMMENT
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Conjecture: All numbers in this sequence are products of two sums of two squares, e.g. 4181 = 37*113 = (1^2+6^2)(7^2+8^2), 1346269=557*2417 = (14^2+19^2)(4^2+49^2).
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MATHEMATICA
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k = {}; Do[If[ !PrimeQ[Fibonacci[Prime[n]]], c = Length[FactorInteger[Fibonacci[Prime[n]]]]; If[c == 2, AppendTo[k, Fibonacci[Prime[n]]]]], {n, 1, 50}]; k
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CROSSREFS
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Cf. A000045, A001605, A050937, A075737, A090819, A134787, A134851, A134852, A135954, A135955, A135956, A135957.
Sequence in context: A045728 A048593 A050937 this_sequence A152511 A103614 A020438
Adjacent sequences: A135950 A135951 A135952 this_sequence A135954 A135955 A135956
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KEYWORD
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nonn
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AUTHOR
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Artur Jasinski (grafix(AT)csl.pl), Dec 08 2007
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