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 A204521 #19 Jul 10 2015 20:12:14 %S A204521 0,0,0,1,3,4,8,21,55,72,144,377,987,1292,2584,6765,17711,23184,46368, %T A204521 121393,317811,416020,832040,2178309,5702887,7465176 %N A204521 Square root of floor(A055812(n) / 5). %C A204521 Or: Numbers whose square yields another square when written in base 5. %C A204521 (For the first 3 terms, the above "base 5" interpretation is questionable, since they have only 1 digit in base 5. It is understood that dropping this digit yields 0.) %C A204521 Base-5 analog of A031150 [base 10], A001353 [base 3], A001542 [base 2]. %C A204521 The square roots of A055812 are listed in A204520. %F A204521 Empirical g.f.: x^4*(x^5+3*x^4+8*x^3+4*x^2+3*x+1) / ((x^4-4*x^2-1)*(x^4+4*x^2-1)). - _Colin Barker_, Sep 15 2014 %o A204521 (PARI) b=5;for(n=1,2e9,issquare(n^2\b) && print1(sqrtint(n^2\b),",")) %Y A204521 Cf. A055792, A055793, A204519, A204517, A204512, A204503 and A023110. %K A204521 nonn %O A204521 1,5 %A A204521 _M. F. Hasler_, Jan 15 2012