OFFSET
1,1
COMMENTS
Squares are congruent to {0, 1, 4, 7} modulo 9, but the reverse is not always true since there are nonsquares that have the same congruence property. See Beiler.
REFERENCES
Albert H. Beiler, Recreations in the theory of numbers, New York, Dover, (2nd ed.) 1966. See p. 140.
MATHEMATICA
Select[Range[0, 162], !IntegerQ[Sqrt[#]] && MemberQ[{0, 1, 4, 7}, Mod[#, 9]] &]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Stefano Spezia, Aug 05 2024
STATUS
approved