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

7, 13, 15, 23, 25, 28, 31, 37, 39, 47, 52, 55, 58, 60, 63, 71, 79, 85, 87, 92, 95, 100, 103, 111, 112, 119, 124, 127, 130, 135, 143, 148, 151, 156, 159, 167, 175, 183, 188, 191, 199, 207, 208, 215, 220, 223, 231, 232, 239, 240, 247, 252, 255, 263, 271, 279, 284

Offset

1,1

Links

Table of n, a(n) for n=1..57.

Example

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

Prog

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

Crossrefs

Cf. A000408, A005767.

Sequence in context: A371784 A293576 A233301 * A233747 A279831 A102797

Adjacent sequences: A274252 A274253 A274254 * A274256 A274257 A274258

Keyword

nonn,easy

Author

Altug Alkan, Jun 16 2016

Status

approved