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Search: id:A133948
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| A133948 |
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a(n) = the number of "isolated divisors" of n(n+1). A positive divisor, k, of n is isolated if neither (k-1) nor (k+1) divides n. |
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+0
3
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| 0, 1, 2, 2, 3, 3, 4, 6, 5, 4, 6, 6, 4, 8, 12, 6, 7, 7, 6, 13, 9, 4, 10, 16, 8, 11, 16, 8, 9, 9, 8, 16, 11, 12, 21, 12, 4, 11, 22, 10, 9, 9, 8, 24, 15, 4, 14, 21, 14, 17, 16, 8, 11, 22, 22, 23, 11, 4, 16, 16, 4, 17, 32, 22, 23, 11, 8, 18, 22, 12, 16, 16, 4, 17, 26, 20, 21, 11, 14, 37, 15, 4, 16
(list; graph; listen)
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OFFSET
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1,3
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LINKS
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Ray Chandler, Table of n, a(n) for n=1..10000
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FORMULA
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a(n) = A092517(n) - A133947(n) = A132881(A002378(n)).
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MATHEMATICA
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Table[Length[Divisors[n*(n + 1)]] - Length[Select[Divisors[n*(n + 1)], If[ # > 1, Mod[n*(n + 1), #*(# - 1)] == 0] || Mod[n*(n + 1), #*(# + 1)] == 0 &]], {n, 1, 80}] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Nov 01 2007
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CROSSREFS
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Cf. A133947, A133950, A092517.
Sequence in context: A089047 A036811 A059185 this_sequence A078935 A129768 A072926
Adjacent sequences: A133945 A133946 A133947 this_sequence A133949 A133950 A133951
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Sep 30 2007
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Nov 01 2007
Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Jun 23 2008
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