OFFSET
1,2
COMMENTS
Heath-Brown proves that a(n) <= 3 for all large n. It seems that n > 119 suffices. - Charles R Greathouse IV, Nov 19 2012
REFERENCES
D. R. Heath-Brown, Ternary quadratic forms and sums of three square-full numbers, Séminaire de Théorie des Nombres, Paris 1986-87, pp. 137-163; Progr. Math., 75, Birkhäuser Boston, Boston, MA, 1988.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
The powerful numbers (A001694) start 1,4,8,9,... 11=1+1+9 and is not the sum of fewer terms, so a(11)=3.
PROG
(PARI) W=vector(99); W[1]=1; for(n=2, #W, if(ispowerful(n), W[n]=1; next); b=n; for(i=1, n\2, b=min(b, W[i]+W[n-i])); W[n]=b); W \\ Charles R Greathouse IV, Nov 19 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Jud McCranie, Jul 13 2001
STATUS
approved