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Search: id:A158187
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| 1, 11, 41, 91, 161, 251, 361, 491, 641, 811, 1001, 1211, 1441, 1691, 1961, 2251, 2561, 2891, 3241, 3611, 4001, 4411, 4841, 5291, 5761, 6251, 6761, 7291, 7841, 8411, 9001, 9611, 10241, 10891, 11561, 12251, 12961, 13691, 14441, 15211, 16001, 16811, 17641
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OFFSET
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0,2
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COMMENT
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a(n) = A033583(n) + 1;
for n>0: a(n) = A010010(n)/2.
If A=[A158445] 25*n.^2+5 (n>0, 30, 105, 230,.,); Y=[A005843] 2*n (n>0, 2, 4, 6,.,); X = [A158187] 10*n^2+1 (n>0, 11, 41,91, .,), we have, for all terms, Pell's equation X^2-A*Y^2=1. Example: 11^2-30*2^2=1; 41^2-105*4^2=1; 91^2-230*6^2=1. [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 19 2009]
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FORMULA
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a(n)=20*n+a(n-1)-30 (with a(1)=1) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 16 2009]
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EXAMPLE
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For n=2, a(2)=20*2+1-30=11; n=3, a(3)=20*3+11-30=41; n=4, a(4)=20*4+41-30=91 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 16 2009]
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CROSSREFS
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C. A158445, A005843 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 19 2009]
Sequence in context: A132232 A031389 A097991 this_sequence A065145 A030685 A132208
Adjacent sequences: A158184 A158185 A158186 this_sequence A158188 A158189 A158190
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KEYWORD
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nonn,new
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Mar 13 2009
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