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Search: id:A133947
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| A133947 |
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a(n) = the number of "non-isolated divisors" of n(n+1). A positive divisor, k, of n is non-isolated if (k-1) or (k+1) also divides n. |
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+0
3
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| 2, 3, 4, 4, 5, 5, 4, 6, 7, 4, 6, 6, 4, 8, 8, 4, 5, 5, 6, 11, 7, 4, 6, 8, 4, 5, 8, 4, 7, 7, 4, 8, 5, 4, 15, 6, 4, 5, 10, 6, 7, 7, 4, 12, 9, 4, 6, 9, 4, 7, 8, 4, 5, 10, 10, 9, 5, 4, 8, 8, 4, 7, 10, 6, 9, 5, 4, 6, 10, 4, 8, 8, 4, 7, 10, 4, 11, 5, 6, 13, 5, 4, 8, 15, 4, 5, 8, 4, 9, 13, 6, 6, 5, 4, 12, 6, 4, 9
(list; graph; listen)
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OFFSET
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1,1
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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) - A133948(n) = A132747(A002378(n)).
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MATHEMATICA
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Table[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. A133948, A133949, A092517.
Sequence in context: A110007 A088527 A030602 this_sequence A060197 A116487 A070546
Adjacent sequences: A133944 A133945 A133946 this_sequence A133948 A133949 A133950
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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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