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A085986 Square 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

A085986 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. [From R. J. Mathar, Sep 12 2008]

LINKS

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

FORMULA

A085986(n) = A006881(n)^2.

EXAMPLE

A006881 begins 6 10 14 15 ...

so A085986 begins 36 100 196 225 ...

MATHEMATICA

f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 2}; Select[Range[20000], f] [From 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 A163246 A014738

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 October 22 11:45 EDT 2014. Contains 248397 sequences.