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Search: id:A118854
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| A118854 |
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Numbers m such that m-1 and m have the same number of common totatives as m and m+1 have. |
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+0
3
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| 2, 3, 8, 21, 24, 27, 45, 75, 93, 105, 117, 123, 147, 165, 213, 309, 315, 333, 357, 387, 453, 525, 555, 573, 627, 636, 693, 717, 729, 765, 795, 843, 915, 933, 957, 1005, 1083, 1125, 1173, 1227, 1323, 1347, 1437, 1467, 1515, 1563, 1575, 1677, 1725, 1755, 1773
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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A057475(a(n)-1) = A057475(a(n));
it seems that even values are very rare, see A118855.
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LINKS
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Eric Weisstein's World of Mathematics, Totative
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EXAMPLE
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n = 21, the sets of totatives for 21-1, 21, and 21+1:
T(20) = {1,3,7,9,11,13,17,19},
T(21) = {1,2,4,5,8,10,11,13,16,17,19,20},
T(22) = {1,3,5,7,9,13,15,17,19,21},
A057475(20) = #intersect(T(20),T(21)) = #{1,11,13,17,19} = 5,
A057475(20) = #intersect(T(21),T(22)) = #{1,5,13,17,19} = 5,
therefore 21 is a term.
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CROSSREFS
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Sequence in context: A066051 A056971 A108125 this_sequence A137652 A122263 A132730
Adjacent sequences: A118851 A118852 A118853 this_sequence A118855 A118856 A118857
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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), May 02 2006
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