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A285800 Numbers having more than one odd prime factor to an odd power in their prime factorization. 2
15, 21, 30, 33, 35, 39, 42, 51, 55, 57, 60, 65, 66, 69, 70, 77, 78, 84, 85, 87, 91, 93, 95, 102, 105, 110, 111, 114, 115, 119, 120, 123, 129, 130, 132, 133, 135, 138, 140, 141, 143, 145, 154, 155, 156, 159, 161, 165, 168, 170, 174, 177, 182, 183, 185, 186 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sequence is of asymptotic density one, a(n) ~ n.

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..19999

EXAMPLE

15 = 3*5, 21 = 3*7, 30 = 2*15, 33 = 3*11 are the smallest positive integers having at least two prime factors to an odd power in their factorization.

a(10) = 57, a(100) = 287, a(10^3) = 1950, a(10^4) = 15701, a(10^5) = 138540, a(10^6) = 1284998.

MAPLE

s800:=[]; s801:=[1];

for n from 2 to 1000 do

c:=0;

t2:=ifactors(n)[2];

for t3 in t2 do if t3[1]>2 and (t3[2] mod 2 = 1) then c:=c+1; fi; od:

if c <= 1 then s801:=[op(s801), n]; else s800:=[op(s800), n]; fi;

od:

s800; # A285800

s801; # A285801 - N. J. A. Sloane, Sep 30 2017

PROG

(PARI) is(n)=1<#select(t->bittest(t, 0), factor(n>>valuation(n, 2))[, 2])

CROSSREFS

Subsequence of A248150.

Complement of A285801.

Sequence in context: A195527 A047200 A070537 * A184041 A070005 A275384

Adjacent sequences:  A285797 A285798 A285799 * A285801 A285802 A285803

KEYWORD

nonn,easy

AUTHOR

M. F. Hasler, Apr 26 2017

STATUS

approved

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Last modified October 21 11:10 EDT 2018. Contains 316414 sequences. (Running on oeis4.)