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Search: id:A105935
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| A105935 |
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Indices of Lucas 7-step numbers A104621 which have a nontrivial divisor in common with index. |
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+0
1
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| 6, 12, 18, 20, 36, 42, 54, 57, 60, 65, 87, 93, 99, 100, 104, 105, 108
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Wanted: closed-form formula for this as exists for Fibonacci and Lucas numbers. Lucas 7-step numbers also known as heptanacci-Lucas numbers. The prime Lucas 7-step numbers are A105768, their indices being A104622.
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FORMULA
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gcd(a(n), A104621(a(n))) > 1.
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EXAMPLE
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gcd(a(n), A104621(6,12,18,36,57,60,87,93,108)) = 3,
gcd(a(n), A104621(20,65,100,105)) = 5,
gcd(a(n), A104621(42)) = 7,
gcd(a(n), A104621(54,99)) = 9,
gcd(a(n), A104621(104)) = 13.
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CROSSREFS
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Cf. A104621, A105285, A105289.
Sequence in context: A094519 A088723 A138939 this_sequence A046411 A037981 A044846
Adjacent sequences: A105932 A105933 A105934 this_sequence A105936 A105937 A105938
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Apr 26 2005
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