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Search: id:A036457
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| A036457 |
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For all a[ n ] if the divisor-number function is iteratively applied exactly 5 times, then the result is independently of n is 2, the fixed point of iteration of d. |
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2
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| 60, 72, 84, 90, 96, 108, 126, 132, 140, 150, 156, 160, 180, 198, 200, 204, 220, 224, 228, 234, 240, 252, 260, 276, 288, 294, 300, 306, 308, 315, 336, 340, 342, 348, 350, 352, 360, 364, 372, 380, 392, 396, 414, 416, 420, 432, 444, 450, 460, 468, 476, 480
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The similarity of this and A030630 is strong but number of divisors here are not only equal to 12 but other values of A036456 also occur.
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FORMULA
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d[ d[ d[ d[ d[ a[ n ] ] ] ] ] ] = 2 for all n
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EXAMPLE
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a[ 13 ]=180, the successive iterates are 18,6,4,3 and finally the 5th is 2; alternatively a[ 3 ]=84 and divisor numbers are 12,6,4,3 and 2.
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CROSSREFS
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A007624, A036450, A046452, A036453, A036455, A030630.
Sequence in context: A080862 A106130 A131564 this_sequence A030630 A068350 A114837
Adjacent sequences: A036454 A036455 A036456 this_sequence A036458 A036459 A036460
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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)
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