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%I #15 Jan 23 2020 16:35:23
%S 7,15,23,87,111,119
%N Numbers that are not the sum of at most three powerful (1) numbers.
%C Mollin and Walsh conjectured that there are no further terms.
%C Heath-Brown proved that the sequence is finite.
%C No other terms less than 40000000. - Paul.Jobling(AT)WhiteCross.com, May 14 2001
%D Heath-Brown, D. R. "Ternary Quadratic Forms and Sums of Three Square-Full Numbers." In Seminaire de Theorie des Nombres, Paris 1986-87 (Ed. C. Goldstein). Boston, MA: Birkhauser, pp. 137-163, 1988.
%H R. A. Mollin and P. G. Walsh, <a href="http://dx.doi.org/10.1155/S0161171286000984">On Powerful Numbers</a>, Intern. J. Math. and Math. Sci, 9:801-806, 1986.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PowerfulNumber.html">Powerful Number.</a>
%e Smallest powerful numbers are 1, 4, 8, 9, 16, 25,... so 7, 15 and 23 are not the sum of one, two or three of them.
%Y Cf. A001694, A076871.
%K fini,nonn
%O 1,1
%A _Henry Bottomley_, Aug 30 2000
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