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Search: id:A000348
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| A000348 |
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Number of ways to pair up {1^2, 2^2, ..., (2n)^2 } so sum of each pair is prime. |
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+0
2
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| 1, 1, 2, 4, 12, 9, 72, 160, 428, 2434, 3011, 10337, 126962, 264182, 783550, 5004266, 34340141, 176302123, 1188146567, 4457147441, 7845512385, 132253267889, 1004345333251, 3865703506342
(list; graph; listen)
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OFFSET
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1,3
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LINKS
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L. E. Greenfield and S. J. Greenfield, Some Problems of Combinatorial Number Theory Related to Bertrand's Postulate, J. Integer Sequences, 1998, #98.1.2.
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FORMULA
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a(n)=permanent(m), where the n-by-n matrix m is defined m(i,j) = 1 or 0, depending on whether (2i)^2+(2j-1)^2 is prime or composite, respectively. - T. D. Noe (noe(AT)sspectra.com), Feb 10 2007
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PROGRAM
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(PARI) permRWNb(a)=n=matsize(a)[1]; if(n==1, return(a[1, 1])); sg=1; nc=0; in=vectorv(n); x=in; x=a[, n]-sum(j=1, n, a[, j])/2; p=prod(i=1, n, x[i]); for(k=1, 2^(n-1)-1, sg=-sg; j=valuation(k, 2)+1; z=1-2*in[j]; in[j]+=z; nc+=z; x+=z*a[, j]; p+=prod(i=1, n, x[i], sg)); return(2*(2*(n%2)-1)*p) for(n=1, 24, a=matrix(n, n, i, j, isprime((2*i)^2+(2*j-1)^2)); print1(permRWNb(a)", ")) - Herman Jamke (hermanjamke(AT)fastmail.fm), May 13 2007
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CROSSREFS
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Cf. A000341.
Sequence in context: A070314 A075554 A137369 this_sequence A141668 A087796 A039587
Adjacent sequences: A000345 A000346 A000347 this_sequence A000349 A000350 A000351
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KEYWORD
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nonn,nice
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AUTHOR
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greenfie(AT)math.rutgers.edu (S. J. Greenfield)
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EXTENSIONS
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More terms from David W. Wilson (davidwwilson(AT)comcast.net).
More terms from T. D. Noe (noe(AT)sspectra.com), Feb 10 2007
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), May 13 2007
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