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Search: id:A131371
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| A131371 |
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Number of anagrams of n that are semiprimes. |
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+0
2
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| 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 2, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 2, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 2, 0, 1, 0, 1, 0, 0, 1, 1, 0, 2, 0, 2, 1, 1, 0, 1, 1, 1, 2, 1, 0, 0, 2, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 1, 0, 2, 1, 1, 0, 0, 0, 1, 0, 2, 2, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1
(list; graph; listen)
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OFFSET
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1,15
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COMMENT
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An anagram of a k-digit number is one of the k! permutations of the digits that does not begin with 0. This is to semiprimes A001358 as A046810 is to primes A000040.
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EXAMPLE
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a(123) = 3 because 123 = 3 * 41 is semiprime, 213 = 3 * 71 is semiprime, 321 = 3 * 107 is semiprime, while the other anagrams 132, 231, and 312 have respectively 3, 3, and 5 prime factors with multiplicity.
a(129) = 4 because 129 = 3 * 43 is semiprime, 219 = 3 * 73 is semiprime, 291 = 3 * 97 is semiprime, 921 = 3 * 307 is semiprime, while 192 and 912 have 7 and 6 prime factors with multiplicity.
a(134) = 5 because 134 = 2 * 67, and 143 = 11 * 13, and 314 = 2 * 157, and 341 = 11 * 31, and 413 = 7 * 59 are semiprimes, while 431 is prime.
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CROSSREFS
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Cf. A000040, A001358, A002113, A046810, A097393.
Sequence in context: A081212 A085491 A116681 this_sequence A003475 A135767 A070203
Adjacent sequences: A131368 A131369 A131370 this_sequence A131372 A131373 A131374
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KEYWORD
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base,easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Sep 30 2007
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