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Search: id:A003057
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| 2, 3, 3, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14
(list; graph; listen)
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OFFSET
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2,1
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COMMENT
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The PARI functions t1, t2 can be used to read a triangular array T(n,k) (n >= 2, 1 <= k <= n-1) by rows from left to right: n -> T(t1(n), t2(n)). - Michael Somos, Aug 23, 2002
a(n) = A002260(n) + A004736(n)
Smallest integer such that n <= (a(n) choose 2). - Frank Ruskey (ruskey(AT)cs.uvic.ca), Nov 06 2007
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LINKS
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M. Somos, Sequences used for indexing triangular or square arrays
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FORMULA
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a(n)=A002024(n-1)+1=round(sqrt(2*(n-1)))+1 - Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 21 2003
a(n) = ceiling( (1+sqrt(1+8n))/2 ). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Aug 28 2001 [Corrected by Frank Ruskey (ruskey(AT)cs.uvic.ca), Nov 06 2007]
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PROGRAM
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(PARI) t1(n)=floor(3/2+sqrt(2*n-2)) /* A003057 */
(PARI) t2(n)=n-1-binomial(floor(1/2+sqrt(2*n-2)), 2) /* A002260(n-2) */
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CROSSREFS
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Cf. A002024, A002260.
Sequence in context: A039836 A083398 A061420 this_sequence A046693 A058889 A110862
Adjacent sequences: A003054 A003055 A003056 this_sequence A003058 A003059 A003060
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KEYWORD
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nonn,easy
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AUTHOR
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njas
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EXTENSIONS
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More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 21 2003
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