The On-Line Encyclopedia of Integer Sequences (OEIS)

The OEIS is supported by the many generous donors to the OEIS Foundation.

Revision History for A053858

(Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A053858

Squarefree even composite numbers with an odd number of prime factors.
(history; published version)

#15 by Harvey P. Dale at Tue May 21 14:14:36 EDT 2024

STATUS

editing

approved

#14 by Harvey P. Dale at Tue May 21 14:14:33 EDT 2024

COMMENTS

Prime factors counted with multiplicity. - Harvey P. Dale, May 21 2024

MATHEMATICA

Select[Range[2, 602, 2], CompositeQ[#]&&SquareFreeQ[#]&&OddQ[PrimeOmega[#]]&] (* Harvey P. Dale, May 21 2024 *)

STATUS

approved

editing

#13 by Charles R Greathouse IV at Tue Aug 29 22:21:44 EDT 2017

STATUS

editing

approved

#12 by Charles R Greathouse IV at Tue Aug 29 22:21:33 EDT 2017

CROSSREFS

A075819 is a subsequence. Intersection of A075819 and A026424, A039956, and A002808.

STATUS

approved

editing

#11 by Charles R Greathouse IV at Tue Aug 29 22:18:13 EDT 2017

STATUS

editing

approved

#10 by Charles R Greathouse IV at Tue Aug 29 22:18:11 EDT 2017

CROSSREFS

A075819 is a subsequence. Intersection of A075819 (or A007304) and A026424.

#9 by Charles R Greathouse IV at Tue Aug 29 22:17:46 EDT 2017

CROSSREFS

A075819 is a subsequence. Intersection of A075819 (or A007304) and A026424.

#8 by Charles R Greathouse IV at Tue Aug 29 22:15:06 EDT 2017

NAME

Even Squarefree even composite numbers n with an odd number of prime factors.

LINKS

Charles R Greathouse IV, <a href="/A053858/b053858.txt">Table of n, a(n) for n = 1..10000</a>

FORMULA

Even numbers n where mu(n) = -1

EXAMPLE

a(3)=66 because 66 is even and its prime divisors are 2, 3 and 11, an odd number.

PROG

(PARI) is(n, f=factor(n))=n%2==0 && #f[, 2]>2 && vecmax(f[, 2])==1 && (#f[, 2])%2 \\ Charles R Greathouse IV, Aug 29 2017

EXTENSIONS

Name corrected by Charles R Greathouse IV, Aug 29 2017

STATUS

approved

editing

#7 by Russ Cox at Sat Mar 31 10:32:39 EDT 2012

AUTHOR

_Enoch Haga (Enokh(AT)comcast.net), _, Mar 28 2000

Discussion

Sat Mar 31

10:32

OEIS Server: https://oeis.org/edit/global/789

#6 by N. J. A. Sloane at Fri Feb 27 03:00:00 EST 2009

EXAMPLE

a(3)=66 because 66 is even and prime divisors are 2, 3, and 11, an odd number.

KEYWORD

easy,nonn,new