%I

%S 9,21,31,43,55,89

%N Positive integers that cannot be expressed using four pentagonal numbers.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PentagonalNumber.html">Pentagonal Number</a>

%Y Cf. A000326, A007527.

%K nonn,fini

%O 1,1

%A _Eric W. Weisstein_, Sep 29 2007