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A085986 Squares of the squarefree semiprimes. 32
36, 100, 196, 225, 441, 484, 676, 1089, 1156, 1225, 1444, 1521, 2116, 2601, 3025, 3249, 3364, 3844, 4225, 4761, 5476, 5929, 6724, 7225, 7396, 7569, 8281, 8649, 8836, 9025, 11236, 12321, 13225, 13924, 14161, 14884, 15129, 16641, 17689, 17956, 19881 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence is a member of a family of sequences directly related to A025487. First terms and known sequences are listed below: 1, A000007; 2, A000040; 4, A001248; 6, A006881; 8, A030078; 12, A054753; 16, A030514; 24, A065036; 30, A007304; 32, A050997; 36, this sequence; 48, ?; 60, ?; 64, ?; ....

Subsequence of A077448. The numbers in A077448 but not in here are 1, the squares of A046386, the squares of A067885, etc. - R. J. Mathar, Sep 12 2008

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A006881(n)^2.

EXAMPLE

A006881 begins 6 10 14 15 ... so this sequence begins 36 100 196 225 ...

MATHEMATICA

f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 2}; Select[Range[20000], f] (* Vladimir Joseph Stephan Orlovsky, Aug 14 2009 *)

Select[Range[200], PrimeOmega[#]==2&&SquareFreeQ[#]&]^2 (* Harvey P. Dale, Mar 07 2013 *)

PROG

(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim\4)^(1/4), t=p^2; forprime(q=p+1, sqrt(lim\t), listput(v, t*q^2))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 20 2011

CROSSREFS

Subsequence of A036785 and of A077448.

Cf. A025487.

Sequence in context: A030627 A177492 A077448 * A027603 A250813 A163246

Adjacent sequences:  A085983 A085984 A085985 * A085987 A085988 A085989

KEYWORD

easy,nonn

AUTHOR

Alford Arnold, Jul 06 2003

STATUS

approved

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Last modified September 1 14:06 EDT 2015. Contains 261270 sequences.