1,1

a(n) = minimal degree of an equation from which n successive terms after the first can be removed (by a series of transformation comparable to Tschirnhaus') without requiring the solution of an equation of degree greater than n (and excluding cases where an equation of degree greater than n is needed but is in fact factorizable into several equations of degree all less than n). Hamilton computed the first six terms of this sequence (see reference). That is the reason why Sylvester and Hammond named them "Hamilton numbers". - Olivier GERARD (olivier.gerard(AT)gmail.com), Oct 17 2007

Raymond Garver, The Tschinrhaus transformation, The Annals of Mathematics, 2nd Ser., Vol. 29, No. 1/4. (1927 - 1928), pp. 329.

W. R. Hamilton, Sixth Report of the British Association for the Advancement of Science, London, 183i, 295-348.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

J. J. Sylvester and M. J. Hammond, On Hamilton's numbers, Phil. Trans. Roy. Soc., 178 (1887), 285-312.

E. Lucas, Th\'{e}orie des Nombres. Gauthier-Villars, Paris, 1891, Vol. 1, p. 496.

a(1)=2 is the familiar fact than one can always remove the linear term of a quadratic equation.

a(2)=3 because one can put any cubic equation in the form x^3-a=0 by a Tschirnhaus transformation based on the solutions of a quadratic equation.

a(4)=11 because one can remove the 4 terms after the first term in a polynomial of degree 11 without having to solve a quintic.

A000905 := proc(n) option remember; local i; if n=1 then 2 else 2+add((-1)^(i+1)*binomial(A000905(n-i), i+1), i=1..n-1); fi; end;

Cf. A001660.

Equals A006719(n) - 1.

Cf. A134294.

Sequence in context: A003686 A086506 A109462 this_sequence A065296 A114895 A083685

Adjacent sequences: A000902 A000903 A000904 this_sequence A000906 A000907 A000908

nonn,nice,easy

N. J. A. Sloane (njas(AT)research.att.com).

The formula given by Lucas on p. 498 is slightly in error - see Maple program given here.