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Search: id:A079427
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| A079427 |
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Least m > n having the same number of divisors as n, a(1)=1. |
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+0
4
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| 1, 3, 5, 9, 7, 8, 11, 10, 25, 14, 13, 18, 17, 15, 21, 81, 19, 20, 23, 28, 22, 26, 29, 30, 49, 27, 33, 32, 31, 40, 37, 44, 34, 35, 38, 100, 41, 39, 46, 42, 43, 54, 47, 45, 50, 51, 53, 80, 121, 52, 55, 63, 59, 56, 57, 66, 58, 62, 61, 72, 67, 65, 68, 729, 69, 70, 71, 75, 74, 78, 73
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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tau(a(n)) = tau(n) and tau(i) <> tau(n), n<i<a(n) (tau=A000005);
a(A000040(k)) = A079428(A000040(k)) = A000040(k+1), as A000005(p)=2 for primes p.
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EXAMPLE
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Sets of divisors for n=10,11,12,13 and 14: D(10)={1,2,5,10}, D(11)={1,11}, D(12)={1,2,3,4,6,12}, D(13)={1,13}, D(14)={1,2,7,14}: therefore a(10)=14 (#D(10)=#D(14)).
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CROSSREFS
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Cf. A112275, A112276.
Sequence in context: A048639 A021282 A016613 this_sequence A081761 A003961 A100463
Adjacent sequences: A079424 A079425 A079426 this_sequence A079428 A079429 A079430
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jan 08 2003
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