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A114601
Number of n X n symmetric positive definite matrices with 2's on the main diagonal and -1, 0, or 1 elsewhere.
2
1, 3, 23, 393, 13089, 737595, 58969079
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OFFSET
1,2
COMMENTS
This gives the number of different values of A + A' where A runs through the matrices counted in
A086215
.
LINKS
Table of n, a(n) for n=1..7.
PROG
(PARI) { a(n) = M=matrix(n, n, i, j, 2*(i==j)); r=0; m=n; b(1); r } { b(k) = if(k>m, r++; return); forvec(x=vector(k-1, i, [-1, 1]), for(i=1, k-1, M[k, i]=M[i, k]=x[i]); if( matdet(vecextract(M, 2^k-1, 2^k-1), 1)>0, b(k+1) ) ) }
CROSSREFS
Cf.
A086215
,
A085657
.
Sequence in context:
A255881
A243195
A233218
*
A178315
A210910
A280654
Adjacent sequences:
A114598
A114599
A114600
*
A114602
A114603
A114604
KEYWORD
hard
,
nonn
,
more
AUTHOR
Max Alekseyev
, Dec 13 2005, Nov 09 2006
STATUS
approved
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Last modified August 5 19:23 EDT 2024. Contains 374954 sequences. (Running on oeis4.)