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%I #17 Aug 24 2023 17:02:43
%S 9,18,25,49,50,98,121,169,242,289,338,361,529,578,722,841,961,1058,
%T 1369,1681,1682,1849,1922,2209,2738,2809,3362,3481,3698,3721,4418,
%U 4489,5041,5329,5618,6241,6889,6962,7442,7921,8978,9409,10082,10201,10609,10658,11449,11881,12482,12769,13778
%N Squares of odd primes and twice squares of odd primes.
%C Essentially, the union of A001248 and A143928.
%C 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 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 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 Cf. A001248, A028982, A143928.
%K nonn,easy
%O 1,1
%A _Wesley Ivan Hurt_, Jul 04 2013
%E a(38) corrected by _Georg Fischer_, Aug 24 2023
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