This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A280965 #17 Feb 27 2017 11:40:07 %S A280965 5,8,40,45,65,80,153,160,200,221,325,360,416,425,493,520,680,725,925, %T A280965 936,1025,1040,1073,1088,1305,1360,1768,1800,1813,1845,1961,2000,2320, %U A280965 2385,2501,2600,2925,3016,3185,3200,3400,3445,3848,3869,3944,3965,4640,4745,5185,5248,5265,5328,5525,5576,5785,5920,6120 %N A280965 Nonsquares whose distances to the two nearest squares are squares. %C A280965 The sequence is infinite because there are terms of it between n^2 and (n+1)^2 whenever 2n+1 is a sum of two squares. %H A280965 Charles R Greathouse IV, <a href="/A280965/b280965.txt">Table of n, a(n) for n = 1..10000</a> %e A280965 a(3) = 40 because the two nearest squares are 36 and 49 and 40 - 36 = 4, 49 - 40 = 9 are both squares. %t A280965 Select[Range[6120], IntegerQ[Sqrt[# - (Floor[Sqrt[#]])^2]] && IntegerQ[Sqrt[(Ceiling[Sqrt[#]])^2 - #]] &] %o A280965 (PARI) is(n)=my(k=sqrtint(n)); issquare(n-k^2) && issquare((k+1)^2-n) && n>k^2 \\ _Charles R Greathouse IV_, Feb 27 2017 %o A280965 (PARI) list(lim)=my(v=List(),k2,K2,n); for(k=2,sqrtint(lim\1)-1, k2=k^2; K2=(k+1)^2; for(s=1,sqrtint(K2-k2-1), n=k2+s^2; if(issquare(K2-n), listput(v,n)))); k2=sqrtint(lim\1)^2; K2=(sqrtint(lim\1)+1)^2; for(n=k2+1,lim, if(issquare(n-k2) && issquare(K2-n), listput(v, n))); Vec(v) \\ _Charles R Greathouse IV_, Feb 27 2017 %Y A280965 Cf. A057653, A234334. %K A280965 nonn %O A280965 1,1 %A A280965 _Emmanuel Vantieghem_, Feb 27 2017