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Search: id:A109321
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| A109321 |
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Admirable numbers n such that the subtracted divisor is > sqrt(n). |
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+0
2
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| 24, 30, 84, 120, 140, 224, 234, 270, 308, 364, 476, 532, 644, 672, 1488, 1638, 2480, 3472, 3724, 4095, 5456, 5624, 6200, 6435, 6448, 8432, 9424, 11408, 14384, 15872, 18352, 20336, 21328, 23312, 24384, 26288, 29264, 29450, 30256, 33232, 35150
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Solutions to sigma(x)=2(x+d) with d>sqrt(x) being a proper divisor of x. The subsequence A165772 contains most of the terms. [From M. F. Hasler (MHasler(AT)univ-ag.fr), Oct 11 2009]
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EXAMPLE
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a(2)=30 because 1+2+3+5+10+15-6 = 30 and 6 > sqrt(30) = 5.477...
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PROGRAM
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(PARI) is_A109321(n)= my(d=sigma(n)-2*n); d>0 && bittest(d, 0)==0 && d<2*n && d*d>4*n && 2*n%d==0 [From M. F. Hasler (MHasler(AT)univ-ag.fr), Oct 11 2009]
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CROSSREFS
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Cf. A111592.
Sequence in context: A141545 A106682 A135045 this_sequence A067952 A123200 A167307
Adjacent sequences: A109318 A109319 A109320 this_sequence A109322 A109323 A109324
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KEYWORD
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nonn
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Aug 20 2005
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