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 A227279 #17 Aug 24 2023 17:02:43 %S A227279 9,18,25,49,50,98,121,169,242,289,338,361,529,578,722,841,961,1058, %T A227279 1369,1681,1682,1849,1922,2209,2738,2809,3362,3481,3698,3721,4418, %U A227279 4489,5041,5329,5618,6241,6889,6962,7442,7921,8978,9409,10082,10201,10609,10658,11449,11881,12482,12769,13778 %N A227279 Squares of odd primes and twice squares of odd primes. %C A227279 Essentially, the union of A001248 and A143928. %C A227279 sigma(a(n)) = (a(n) + sqrt(a(n)) + 1) * (omega(a(n))^2 - omega(a(n)) + 1). omega(a(n)) = 2 - (a(n) mod 2). Omega(a(n)) = 3 - (a(n) mod 2). mu(a(n)) = 0. rad(a(n)) = sqrt( a(n)*omega(a(n)) ). %e A227279 49 is in the sequence since 49 = 7^2 (the square of an odd prime). 18 is in the sequence since 18 = 2*3^2 (twice the square of an odd prime). %t A227279 max = 13778; Union[Prime[Range[2, PrimePi[Sqrt[max]]]]^2, 2Prime[Range[2, PrimePi[Sqrt[max/2]]]]^2] (* _Alonso del Arte_, Jul 04 2013 *) %Y A227279 Cf. A001248, A028982, A143928. %K A227279 nonn,easy %O A227279 1,1 %A A227279 _Wesley Ivan Hurt_, Jul 04 2013 %E A227279 a(38) corrected by _Georg Fischer_, Aug 24 2023