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A120944 Composite squarefree numbers. 44
6, 10, 14, 15, 21, 22, 26, 30, 33, 34, 35, 38, 39, 42, 46, 51, 55, 57, 58, 62, 65, 66, 69, 70, 74, 77, 78, 82, 85, 86, 87, 91, 93, 94, 95, 102, 105, 106, 110, 111, 114, 115, 118, 119, 122, 123, 129, 130, 133, 134, 138, 141, 142, 143, 145, 146, 154, 155, 158, 159, 161 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Intersection of A002808 and A005117: n > 1 such that A008966(n) * (1-A010051(n)) = 1. - Reinhard Zumkeller, Dec 19 2011

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

a(n) are the solutions to floor(omega(x)/bigomega(x))*(1-floor(1/bigomega(x))) = 1, where bigomega is A001222 and omega is A001221. - Enrique Pérez Herrero, Apr 01 2012

Sum_{n>=1} 1/a(n)^s  = Zeta(s)/Zeta(2s) - 1 - PrimeZeta(s). - Enrique Pérez Herrero, Apr 01 2012

MAPLE

select(not(isprime) and numtheory:-issqrfree, [$2..1000]); # Robert Israel, Jul 07 2015

MATHEMATICA

lst={}; Do[If[SquareFreeQ[n], If[ !PrimeQ[n], AppendTo[lst, n]]], {n, 2, 6!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jan 20 2009; updated by Jean-François Alcover, Jun 19 2013 *)

Select[Range[200], PrimeNu[#] > 1 && SquareFreeQ[#] &] (* Carlos Eduardo Olivieri, Jul 07 2015 *)

PROG

(MAGMA) [n: n in [6..161] | IsSquarefree(n) and not IsPrime(n)]; // Bruno Berselli, Mar 03 2011

(Haskell)

a120944 n = a120944_list !! (n-1)

a120944_list = filter ((== 1) . a008966) a002808_list

-- Reinhard Zumkeller, Dec 19 2011

(PARI) is(n)=issquarefree(n)&&!isprime(n)&&n>1 \\ Charles R Greathouse IV, Apr 11 2012

CROSSREFS

Cf. A000469 (Nonprime squarefree numbers).

Cf. A001221, A001222, A002808, A005117, A008966, A010051.

Sequence in context: A212168 A080365 A000469 * A052053 A276818 A238748

Adjacent sequences:  A120941 A120942 A120943 * A120945 A120946 A120947

KEYWORD

nonn

AUTHOR

Zak Seidov, Aug 19 2006

STATUS

approved

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Last modified March 28 05:07 EDT 2017. Contains 284182 sequences.