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 A024556 Odd squarefree composite numbers. 23
 15, 21, 33, 35, 39, 51, 55, 57, 65, 69, 77, 85, 87, 91, 93, 95, 105, 111, 115, 119, 123, 129, 133, 141, 143, 145, 155, 159, 161, 165, 177, 183, 185, 187, 195, 201, 203, 205, 209, 213, 215, 217, 219, 221, 231, 235, 237, 247, 249, 253, 255, 259, 265, 267, 273 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Composite numbers n such that Sum_{k=1..n-1} floor(k^3/n) = (1/4)*(n-2)*(n^2-1) (equality also holds for all primes). - Benoit Cloitre, Dec 08 2002 LINKS Zak Seidov, Table of n, a(n) for n = 1..11999. Eric Weisstein's World of Mathematics, Lehmer's Constant Eric Weisstein's World of Mathematics, Prime Sums MATHEMATICA Complement[Select[Range[3, 281, 2], SquareFreeQ], Prime[Range[PrimePi[281]]]] (* Harvey P. Dale, Jan 26 2011 *) PROG (Haskell) a024556 n = a024556_list !! (n-1) a024556_list = filter ((== 0) . a010051) \$ tail a056911_list -- Reinhard Zumkeller, Apr 12 2012 (PARI) is(n)=n>1&&n%2&&!isprime(n)&&issquarefree(n) \\ Charles R Greathouse IV, Apr 12 2012 (PARI) forstep(n=3, 273, 2, k=omega(n); if(k>1&&bigomega(n)==k, print1(n, ", "))) \\ Hugo Pfoertner, Dec 19 2018 CROSSREFS Intersection of A056911 and A071904. Subsequence of A061346. Cf. A010051, A046388, A078837. Sequence in context: A225375 A329229 A146166 * A046388 A056913 A002557 Adjacent sequences:  A024553 A024554 A024555 * A024557 A024558 A024559 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, May 22 2000 EXTENSIONS More terms from James A. Sellers, May 22 2000 STATUS approved

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Last modified July 27 15:12 EDT 2021. Contains 346307 sequences. (Running on oeis4.)