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Search: id:A063380
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| A063380 |
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a(1) = 4, a(n) = concatenation of two closest factors of a(n-1) whose product equals a(n-1) or if a(n-1) is a prime then the concatenation of 1 and a(n-1). |
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1
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| 4, 22, 211, 1211, 7173, 9797, 97101, 910789, 1182799, 1319029, 6719687, 7678761, 32559587, 257126691, 1591617149, 6653239233, 62767105999, 126149775659, 432933715713, 2435717774509, 6598336914323, 19495633384521
(list; graph; listen)
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OFFSET
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1,1
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MATHEMATICA
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f[ n_Integer ] := (d = Divisors[ n ]; l = Length[ d ]; If[ EvenQ[ l ], ToExpression[ ToString[ d[ [ l/2 ] ] ] <> ToString[ d[ [ l/2 + 1 ] ] ] ], ToExpression[ ToString[ d[ [ l/2 + .5 ] ] ] <> ToString[ d[ [ l/2 + .5 ] ] ] ] ] ); NestList[ f, 4, 24 ]
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CROSSREFS
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Cf. A003681, A062094 and A062095.
Sequence in context: A002728 A062494 A103437 this_sequence A113385 A120482 A137158
Adjacent sequences: A063377 A063378 A063379 this_sequence A063381 A063382 A063383
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KEYWORD
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base,nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 08 2001
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