login
A069741
Let M_n be the n X n matrix M_(i,j)=1/(2^i+2^j), then a(n) is the numerator of det(M_n).
1
1, 1, 1, 49, 2401, 113060689, 260871824431729, 9708455965188246321478801, 361304320362377236050632364626862769, 3511057522394397982450601057907077808699210592028881
OFFSET
1,4
COMMENTS
a(n) seems always to be a square and 7 seems to follow a rule in a(n) factorization. Maximal k such that 7^k divides a(n) are 0, 0, 0, 2, 4, 6, 10, 14, 18, 24, 30, 36, 44, 52, 60, 70, 80, 90, 102, 114, 126, 142, 158, 174, 192... Hence if b(n)=maximum exponent of 7 in factorization of a(n), b(3n+1)=A049450(n); b(3n+2)=A049450(n)+2*n; b(3n+3)=A049450(n)+4n
LINKS
PROG
(PARI) for(n=1, 70, print1(numerator(matdet(matrix(n, n, i, j, 1/(2^i+2^j)))), ", "))
CROSSREFS
Cf. A069743.
Sequence in context: A218751 A120999 A087752 * A203384 A099367 A307811
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Apr 21 2002
STATUS
approved