cp's OEIS Frontend

A226025 Odd composite numbers that are not squares of primes.

%I A226025 #66 Jul 01 2025 21:40:06
%S A226025 15,21,27,33,35,39,45,51,55,57,63,65,69,75,77,81,85,87,91,93,95,99,
%T A226025 105,111,115,117,119,123,125,129,133,135,141,143,145,147,153,155,159,
%U A226025 161,165,171,175,177,183,185,187,189,195,201,203,205,207,209,213,215,217
%N A226025 Odd composite numbers that are not squares of primes.
%C A226025 Numbers that are in A071904 (odd composite numbers) but not in A001248 (squares of primes).
%C A226025 First differs from its subsequence A082686 in a(16)=81 which is not in A082686. More precisely, A226025 \ A082686 = A062532 \ {1} = A014076^2 \ {1}. - _M. F. Hasler_, Oct 20 2013
%C A226025 Odd numbers that are greater than the square of their least prime factor - _Odimar Fabeny_, Sep 08 2014
%H A226025 Arkadiusz Wesolowski, <a href="/A226025/b226025.txt">Table of n, a(n) for n = 1..10000</a>
%F A226025 A226025 = { odd x>1 | A100995(x) = 0 or A100995(x) > 2 }. - _M. F. Hasler_, Oct 20 2013
%p A226025 select(n -> not(isprime(n)) and (not(issqr(n)) or not(isprime(sqrt(n)))), [seq(2*i+1,i=1..1000)]); # _Robert Israel_, Sep 08 2014
%t A226025 Select[Range[3, 217, 2], ! PrimeQ[#] && ! PrimeQ@Sqrt[#] &]
%t A226025 r = Prime@Range[2, 6]^2; Complement[Select[Range[3, Last[r] - 2, 2], ! PrimeQ[#] &], Most[r]]
%t A226025 Select[Range[3,251,2],NoneTrue[{#,Sqrt[#]},PrimeQ]&] (* _Harvey P. Dale_, Sep 06 2021 *)
%o A226025 (Magma) [n: n in [3..217 by 2] | not IsPrime(n) and not IsSquare(n) or IsSquare(n) and not IsPrime(Floor(n^(1/2)))];
%o A226025 (Haskell)
%o A226025 a226025 n = a226025_list !! (n-1)
%o A226025 a226025_list = filter ((/= 2) . a100995) a071904_list
%o A226025 -- _Reinhard Zumkeller_, Jun 15 2013
%o A226025 (PARI) is_A226025(n)={bittest(n,0)&&!isprime(n,0)&&!(issquare(n)&&isprime(sqrtint(n)))&&n>1} \\ - _M. F. Hasler_, Oct 20 2013
%Y A226025 Subsequence of A071904. Cf. A226603.
%K A226025 nonn
%O A226025 1,1
%A A226025 _Arkadiusz Wesolowski_, Jun 07 2013