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Search: id:A030626
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| A030626 |
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Numbers with 8 divisors. |
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+0
20
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| 24, 30, 40, 42, 54, 56, 66, 70, 78, 88, 102, 104, 105, 110, 114, 128, 130, 135, 136, 138, 152, 154, 165, 170, 174, 182, 184, 186, 189, 190, 195, 222, 230, 231, 232, 238, 246, 248, 250, 255, 258, 266, 273, 282, 285, 286, 290, 296, 297, 310, 318
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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R. J. Mathar, Table of n, a(n) for n = 1..634
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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FORMULA
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a(n)= product of a prime and the cube of another prime or a(n) = product of three distinct primes (square-free number with three prime factors) or a(n) = p^7 where p is prime. - Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 21 2001. Case I: a(n) = p^3*q, a(1)= 24 = 2^*3, proper divisor product = 13824=24^3. Case II: a(n) = p*q*r a(2) = 30 = 2*3*5, proper divisor product = 27000=30^3. Case III: a(n) = p^7 a(14) = 128 = 2^7, proper divisor product = 2^21. Here p, q, r are distinct primes.
A000005(a(n))=8. - Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 10 2009
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CROSSREFS
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Essentially the same as A111398.
Cf. A000005. - Juri-Stepan Gerasimov (2stepan(AT)rambler.r), Oct 10 2009
Sequence in context: A129656 A048945 A111398 this_sequence A125639 A076496 A125640
Adjacent sequences: A030623 A030624 A030625 this_sequence A030627 A030628 A030629
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KEYWORD
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nonn
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AUTHOR
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Jeff Burch (jmburch(AT)osprey.smcm.edu)
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