cp's OEIS Frontend

A355490 Numbers of the form a+b+c = a^2 - b^2 - c^2 where a > b >= c > 0.

%I A355490 #34 Jul 05 2022 07:16:21
%S A355490 8,15,20,24,27,32,35,39,44,48,49,51,54,55,56,63,64,65,68,75,80,84,87,
%T A355490 90,92,95,98,99,104,111,114,116,119,120,123,125,128,132,135,140,143,
%U A355490 144,147,152,153,155,159,160,164,168,170,171,174,175,176,183,184,185,188,189,195,200,203,204,207,208,209,212,215,216,219,220,224,230,231
%N A355490 Numbers of the form a+b+c = a^2 - b^2 - c^2 where a > b >= c > 0.
%C A355490 It seems that A082867 is a subsequence.
%C A355490 The first counterexample to the above is A082867(60) = 258. - _Charles R Greathouse IV_, Jul 05 2022
%H A355490 Charles R Greathouse IV, <a href="/A355490/b355490.txt">Table of n, a(n) for n = 1..10000</a>
%e A355490 8 is a term: 8 = 4+2+2 = 4^2 - 2^2 - 2^2.
%e A355490 15 is a term: 15 = 7+5+3 = 7^2 - 5^2 - 3^2.
%t A355490 Solve[a==r^2-s^2-d^2 && 1<=r<=120 && 1<=s<=120 && 1<=d<=120 && 0<=a && r>s>=d && a==r+s+d, {a,r,s,d}, Integers]
%o A355490 (PARI) list(lim)=my(v=List([8]));lim\=1;for(a=3,lim-2,my(a2=a^2);for(b=(sqrt(2*a^2+2*a+1)-1)\2,a-2,my(t=a2-b^2-a-b,s);if(issquare(4*t+1,&s) && (c=(s-1)/2)<=b && c<=b && a+b+c<=lim, listput(v,a+b+c)))); Set(v) \\ _Charles R Greathouse IV_, Jul 05 2022
%Y A355490 Cf. A082867, A082772, A134582, A355491.
%K A355490 nonn
%O A355490 1,1
%A A355490 _Mohammad Arab_, Jul 04 2022
%E A355490 a(57) = 184 inserted by _Charles R Greathouse IV_, Jul 05 2022