easy, hard

[Neil Fernandez]

In message <000b01c1da4d$5e9d7940$9102a8c0 at segmail.com>, Brian L.
Galebach <briang at SEGmail.com> writes
>The help file indicates that it is hard "if the next term is not known".
>However, that doesn't make sense if we know a billion terms.

I'd interpret 'next term' as meaning 'next term after the ones shown'.

>I think that a
>hard sequence should be one for which it becomes very difficult to calculate
>values after just a few terms, (unless the values of the terms are easily
>understood such as A014221 where a(n+1) = 2^a(n) ).

Agreed, this is a nice definition, but maybe "a few terms" could
usefully be taken to mean "the ones shown"? Meanwhile instead of "very
difficult to calculate values" I'd suggest "very difficult to calculate
the next term, or to prove that no further terms exist". See e.g.
A069479.

Neil
-- 
Neil Fernandez