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A069741
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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).
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1
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1, 1, 1, 49, 2401, 113060689, 260871824431729, 9708455965188246321478801, 361304320362377236050632364626862769, 3511057522394397982450601057907077808699210592028881
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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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
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..25
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PROG
| (PARI) for(n=1, 70, print1(numerator(matdet(matrix(n, n, i, j, 1/(2^i+2^j)))), ", "))
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CROSSREFS
| Cf. A069743.
Sequence in context: A170768 A120999 A087752 * A203384 A099367 A123841
Adjacent sequences: A069738 A069739 A069740 * A069742 A069743 A069744
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KEYWORD
| easy,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 21 2002
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