login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A051144 Nonsquarefree nonsquares: each entry has a square factor but is not a perfect square itself. 3
8, 12, 18, 20, 24, 27, 28, 32, 40, 44, 45, 48, 50, 52, 54, 56, 60, 63, 68, 72, 75, 76, 80, 84, 88, 90, 92, 96, 98, 99, 104, 108, 112, 116, 117, 120, 124, 125, 126, 128, 132, 135, 136, 140, 147, 148, 150, 152, 153, 156, 160, 162, 164, 168, 171, 172, 175, 176, 180 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

At least one exponent in canonical prime factorization (cf. A124010) is odd and greater than 1. - Reinhard Zumkeller, Jan 24 2013

LINKS

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

Eric Weisstein's World of Mathematics, Square Number

Eric Weisstein's World of Mathematics, Squarefree

Wikipedia, Squarefree integer

Wikipedia, Square number

FORMULA

(1-A008966(a(n)))*(1-A010052(a(n))) = 1; A008966(a(n))+A010052(a(n)) = 0. - Reinhard Zumkeller, Jan 24 2013

EXAMPLE

65 is not included because it is squarefree. 64 is not included because it is a perfect square. 63 is included because 63 = 3^2 * 7

MAPLE

N:= 10000;  # to get all entries up to N

A051144:= remove(numtheory:-issqrfree, {$1..N}) minus {seq(i^2, i=1..floor(sqrt(N)))}:

# Robert Israel, Mar 30 2014

PROG

(Haskell)

a051144 n = a051144_list !! (n-1)

a051144_list = filter ((== 0) . a008966) a000037_list

-- Reinhard Zumkeller, Sep 02 2013, Jan 24 2013

(PARI) is(n)=!issquare(n) && !issquarefree(n) \\ Charles R Greathouse IV, Sep 18 2015

CROSSREFS

Cf. A210490 (complement), intersection of A013929 and A000037.

Sequence in context: A257162 A104201 A036327 * A067537 A046339 A145784

Adjacent sequences:  A051141 A051142 A051143 * A051145 A051146 A051147

KEYWORD

nonn,easy

AUTHOR

Michael Minic (Rassilon6(AT)aol.com)

EXTENSIONS

Incorrect comment removed by Charles R Greathouse IV, Mar 19 2010

Offset corrected by Reinhard Zumkeller, Jan 24 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 21 15:32 EDT 2019. Contains 323444 sequences. (Running on oeis4.)