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Search: id:A069741
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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; listen)
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OFFSET
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1,4
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COMMENT
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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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PROGRAM
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(PARI) for(n=1, 70, print1(numerator(matdet(matrix(n, n, i, j, 1/(2^i+2^j)))), ", "))
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CROSSREFS
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Cf. A069743.
Sequence in context: A049682 A120999 A087752 this_sequence A099367 A123841 A014773
Adjacent sequences: A069738 A069739 A069740 this_sequence A069742 A069743 A069744
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 21 2002
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