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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A069187 Numbers n such that core(n) = ceiling(sqrt(n)) where core(x) is the squarefree part of x (the smallest integer such that x*core(x) is a square). 2
1, 2, 20, 90, 272, 650, 1332, 4160, 6642, 10100, 14762, 20880, 28730, 38612, 50850, 65792, 83810, 130682, 160400, 194922, 234740, 280370, 332352, 391250, 457652 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Conjecture: sequence is A071253 minus those entries of A071253 that have their index in A049532, i.e., a(n) is of form n^2*(n^2+1) for all n not in A049532. - Ralf Stephan, Aug 18 2004

LINKS

Table of n, a(n) for n=1..25.

MATHEMATICA

core[n_] := Times @@ Apply[ Power, {#[[1]], Mod[#[[2]], 2]}& /@ FactorInteger[n], {1}]; Select[Range[500000], core[#] == Ceiling[Sqrt[#]]&] (* Jean-Fran├žois Alcover, Jul 26 2011 *)

CROSSREFS

Sequence in context: A279264 A063663 A071253 * A033840 A086755 A107483

Adjacent sequences:  A069184 A069185 A069186 * A069188 A069189 A069190

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Apr 14 2002

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified April 25 14:30 EDT 2017. Contains 285414 sequences.