OFFSET
1,2
COMMENTS
Conjecture: the sequence {a(n)^(m/2), n>=1} forms a logarithmic derivative of an integer sequence only when m is a nonnegative even integer.
FORMULA
a(n) = A177431(n)^2.
EXAMPLE
L.g.f.: A(x) = x + 9/2*x^2 + 16/3*x^3 + 25/4*x^4 + 36/5*x^5 +...
exp(A(x)) = 1 + x + 5*x^2 + 10*x^3 + 24*x^4 + 51*x^5 + 122*x^6 + 244*x^7 +...+ A177432(n)*x^n +...
The square-root of each term gives the sequence A177431, which begins:
[1, 3, 4, 5, 6, ...];
A177431 does not form a logarithmic derivative of an integer sequence.
PROG
(PARI) {a(n)=local(V, A=[1], M); V=Vec(exp(x+sum(k=2, n-1, a(k)*x^k/k)+t*x^n/n+x*O(x^n))); if(n==1, M=1, M=a(n-1); for(m=sqrtint(a(n-1))+1, 9*a(n-1), if(denominator(subst(V[ #V], t, m^2))==1, M=m^2; break)); M)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Sep 06 2010
EXTENSIONS
Edited to prevent horizontal scrolling -- Charles R Greathouse IV, Sep 08 2010
STATUS
approved