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 A274255 Numbers n such that n^2 is the sum of three nonzero squares while n is not. 0

%I

%S 7,13,15,23,25,28,31,37,39,47,52,55,58,60,63,71,79,85,87,92,95,100,

%T 103,111,112,119,124,127,130,135,143,148,151,156,159,167,175,183,188,

%U 191,199,207,208,215,220,223,231,232,239,240,247,252,255,263,271,279,284

%N Numbers n such that n^2 is the sum of three nonzero squares while n is not.

%e 7 is a term because 7 is not in A000408 and 7^2 = 49 = 2^2 + 3^2 + 6^2.

%o (PARI) isA000408(n) = my(a, b) ; a=1 ; while(a^2+1<n, b=1 ; while(b<=a && a^2+b^2<n, if(issquare(n-a^2-b^2), return(1) ) ; b++ ; ) ; a++ ; ) ; return(0) ;

%o lista(nn) = for(n=1, nn, if(!isA000408(n) && isA000408(n^2), print1(n, ", ")));

%Y Cf. A000408, A005767.

%K nonn,easy

%O 1,1

%A _Altug Alkan_, Jun 16 2016

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Last modified March 29 13:04 EDT 2023. Contains 361599 sequences. (Running on oeis4.)