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 A231431 #30 Dec 10 2019 04:14:35 %S A231431 0,9,36,144,169,225,441,576,676,729,900,1369,1764,2025,2209,2304,2704, %T A231431 2809,2916,3249,3600,3721,3969,4761,5329,5476,6561,6889,7056,8100, %U A231431 8649,8836,9216,9801,10816,11025,11236,11449,11664,11881,12321,12996,13225,14161,14400,14884,15129,15876,17689,18769,19044,19881,21316,21904 %N A231431 Evil squares. %C A231431 Numbers n^2 such that A159918(n) is even. %C A231431 Intersection of A000290 and A001969. %H A231431 Amiram Eldar, <a href="/A231431/b231431.txt">Table of n, a(n) for n = 1..10000</a> %F A231431 Conjecture: a(n) ~ 4n^2. - _Charles R Greathouse IV_, Nov 20 2013 %e A231431 36 is in the sequence because 36 = 6^2 and 36 in base 2 is 100100, having an even number of 1's. %t A231431 Select[Range[0,150]^2,EvenQ[DigitCount[#,2,1]]&] (* _Harvey P. Dale_, Nov 23 2015 *) %o A231431 (PARI) is(n)=hammingweight(n)%2==0 && issquare(n) \\ _Charles R Greathouse IV_, Nov 20 2013 %Y A231431 Cf. A000290, A125498. %K A231431 nonn,base,easy %O A231431 1,2 %A A231431 _Juri-Stepan Gerasimov_, Nov 20 2013 %E A231431 Corrected and extended by _Harvey P. Dale_, Nov 23 2015