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Search: id:A133949
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| A133949 |
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a(n) = the number of "non-isolated divisors" of n(n+1)/2. A positive divisor k of n is non-isolated if either k-1 or k+1 also divides n. |
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+0
3
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| 0, 0, 3, 2, 0, 0, 2, 4, 0, 0, 3, 3, 0, 0, 6, 2, 0, 0, 2, 8, 0, 0, 4, 6, 0, 0, 5, 2, 0, 0, 2, 6, 0, 0, 10, 3, 0, 0, 8, 4, 0, 0, 2, 8, 0, 0, 4, 7, 0, 0, 3, 2, 0, 0, 6, 6, 0, 0, 5, 5, 0, 0, 8, 4, 0, 0, 2, 3, 0, 0, 4, 4, 0, 0, 5, 2, 0, 0, 4, 9, 0, 0, 5, 10, 0, 0, 6, 2, 0, 0, 4, 3, 0, 0, 10, 4, 0, 0, 8, 2, 0, 0, 2, 13
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OFFSET
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1,3
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COMMENT
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a(k) = 0 for k mod 4 == {1,2}. - Chandler
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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) = A063440(n) - A133950(n) = A132747(A000217(n)).
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MATHEMATICA
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Table[Length[Select[Divisors[n*(n + 1)/2], If[ # > 1, Mod[n*(n + 1)/2, #*(# - 1)] == 0] || Mod[n*(n + 1)/2, #*(# + 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, A063440.
Sequence in context: A036112 A134884 A033909 this_sequence A139808 A055654 A062787
Adjacent sequences: A133946 A133947 A133948 this_sequence A133950 A133951 A133952
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.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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