A270385 - OEIS

%I #13 May 17 2016 12:05:46

%S 25,75,100,150,169,175,195,225,255,275,289,300,350,375,390,400,435,

%T 455,475,507,510,525,550,555,575,595,600,615,663,675,676,700,715,750,

%U 775,780,795,825,841,867,870,875,900,910,915,935,950,975,1014,1015,1020,1050,1075,1095

%N Numbers n such that n^2 is a term of A007692 while n is not.

%C Subsequence of A009177.

%e 25 is a term because 25 is not a term of A007692 while 25^2 = 625 is a term of A007692.

%t fQ[n_] := Length@ Select[PowersRepresentations[n, 2, 2], First@ # != 0 &] > 1; Select[Range@1100, And[! fQ@ #, fQ[#^2]] &] (* _Michael De Vlieger_, May 17 2016 *)

%o (PARI) isA007692(n) = {nb = 0; lim = sqrtint(n); for (x=1, lim, if ((n-x^2 >= x^2) && issquare(n-x^2), nb++); ); nb >= 2; }

%o lista(nn) = for(n=1, nn, if(!isA007692(n) && isA007692(n^2), print1(n, ", ")));

%Y Cf. A007692, A009177.

%K nonn

%O 1,1

%A _Altug Alkan_, May 17 2016