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A001670
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n appears n times (n even).
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5
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2, 2, 4, 4, 4, 4, 6, 6, 6, 6, 6, 6, 8, 8, 8, 8, 8, 8, 8, 8, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 16, 16, 16
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..10000
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FORMULA
| a(n) = 2*floor( 1/2 + sqrt(n)). - Antonio Esposito (antonio.b.esposito(AT)italtel.it), Jan 21 2002
With a different offset: g.f. = Sum(i=0, inf, 2*x^(i^2+i)/(1-x)). - Ralf Stephan (ralf(AT)ark.in-berlin.de), Mar 11 2003
a(1)=2, a(2)=2, a(n)=a(n-a(n-2))+2 [From Branko Curgus (curgus(AT)wwu.edu), May 11 2010]
a(n)=2*round(sqrt(n)) [From Branko Curgus (curgus(AT)wwu.edu), May 11 2010]
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MATHEMATICA
| a[1]=2, a[2]=2, a[n_]:=a[n]=a[n-a[n-2]]+2 [From Branko Curgus (curgus(AT)wwu.edu), May 11 2010]
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PROG
| (MAGMA) [2*Round(Sqrt(n)): n in [1..70]]; // Vincenzo Librandi, Jun 23 2011
(PARI) a(n)=round(sqrt(n))<<1 \\ Charles R Greathouse IV, Jun 23 2011
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CROSSREFS
| Cf. A001650, A000194.
Sequence in context: A080374 A165040 A035683 * A100144 A076222 A177692
Adjacent sequences: A001667 A001668 A001669 * A001671 A001672 A001673
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| The first formula corrected by Branko Curgus (curgus(AT)wwu.edu), May 11 2010
Offset changed from 2 to 1 by Vincenzo Librandi, Jun 23 2011
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