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A102641
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Compute the greatest prime divisors [A006530(),GPD] of -j+2^n for j=0,1,...,L. a(n) is the maximal L length of such a sequence in which the greatest prime divisors are increasing with decreasing j.
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4
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1, 2, 2, 4, 2, 4, 2, 3, 2, 4, 2, 4, 2, 4, 2, 2, 2, 3, 2, 4, 2, 2, 2, 4, 2, 2, 2, 4, 2, 4, 2, 3, 2, 4, 4, 4, 2, 3, 4, 4, 2, 3, 2, 4, 2, 2, 2, 4, 2, 3, 2, 4, 2, 4, 6, 2, 4, 2, 2, 3, 2, 3, 3, 2, 2, 3, 2, 3, 2, 3, 2, 4, 2, 3, 6, 4, 2, 3, 2, 3, 4, 2, 2, 3, 2, 3, 2, 3, 2, 3, 2, 4, 2, 4, 4, 4, 2, 3, 3, 4, 2, 4, 2, 3, 5
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OFFSET
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1,2
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COMMENTS
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A006530(2^n)=2 is a local minimum. Going either upward or downward with the argument, the largest prime factors are increasing for a while. Here the maximal length of increasing largest-prime-divisor sequences are given when going downward with the arguments. Compare with A102640.
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LINKS
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Table of n, a(n) for n=1..105.
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EXAMPLE
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n=12: 2^10=4096. The greatest prime divisors for 4096, 4095, 4094, 4093 are as follows:{2, 13, 89, 4093}. A006530[4092]=31 is already smaller than A006530[4093]. Thus the length of increasing GPD-sequence is 4=a(12).
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CROSSREFS
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Cf. A006530, A102640, A102642, A102643, A102644.
Sequence in context: A131817 A214430 A138232 * A054763 A100374 A045841
Adjacent sequences: A102638 A102639 A102640 * A102642 A102643 A102644
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Jan 21 2005
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STATUS
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approved
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