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A280321 Number of 2 X 2 matrices with all elements in {0,..,n} having determinant = n*permanent. 3
1, 12, 25, 49, 81, 121, 169, 225, 289, 361, 441, 529, 625, 729, 841, 961, 1089, 1225, 1369, 1521, 1681, 1849, 2025, 2209, 2401, 2601, 2809, 3025, 3249, 3481, 3721, 3969, 4225, 4489, 4761, 5041, 5329, 5625, 5929, 6241, 6561, 6889, 7225, 7569, 7921, 8281, 8649, 9025, 9409, 9801, 10201 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Same as A016754, except for n=1. Here a(1)=12 but A016754(1)=9.

LINKS

Indranil Ghosh, Table of n, a(n) for n = 0..990

FORMULA

a(n+1) = (((n-2)*a(n))/(n-1)) + ((12*(n)^2-12*(n)+1)/(n-1)) for n>=1.

Conjectures from Colin Barker, Jan 01 2017: (Start)

a(n) = (1 + 2*n)^2 = A273789(n) = A273743(n) for n>1.

a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>4.

G.f.: (1 + 9*x - 8*x^2 + 9*x^3 - 3*x^4) / (1 - x)^3.

(End)

PROG

(Python)

def t(n):

    s=0

    for a in range(n+1):

        for b in range(n+1):

            for c in range(n+1):

                for d in range(n+1):

                    if (a*d-b*c)==n*(a*d+b*c):

                        s+=1

    return s

for i in range(41):

    print(str(i)+" "+str(t(i)))

CROSSREFS

Cf. A016754.

Sequence in context: A224669 A164577 A195143 * A198274 A229447 A175523

Adjacent sequences:  A280318 A280319 A280320 * A280322 A280323 A280324

KEYWORD

nonn

AUTHOR

Indranil Ghosh, Jan 01 2017

STATUS

approved

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Last modified July 28 16:54 EDT 2021. Contains 346335 sequences. (Running on oeis4.)