This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A069741 #8 Mar 30 2012 18:38:57 %S A069741 1,1,1,49,2401,113060689,260871824431729,9708455965188246321478801, %T A069741 361304320362377236050632364626862769, %U A069741 3511057522394397982450601057907077808699210592028881 %N 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). %C A069741 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 %H A069741 Vincenzo Librandi, <a href="/A069741/b069741.txt">Table of n, a(n) for n = 1..25</a> %o A069741 (PARI) for(n=1,70,print1(numerator(matdet(matrix(n,n,i,j,1/(2^i+2^j)))),",")) %Y A069741 Cf. A069743. %K A069741 easy,nonn %O A069741 1,4 %A A069741 _Benoit Cloitre_, Apr 21 2002