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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A088595 Numbers n such that (A006530(n) + A020639(n))/2 is an integer, divides n and it is not a power of prime number: it has at least 2 distinct prime factors. Special terms of A088948. 4
105, 231, 315, 525, 627, 693, 735, 897, 935, 945, 1155, 1575, 1581, 1617, 1729, 1881, 2079, 2205, 2465, 2541, 2625, 2691, 2835, 2967, 3135, 3465, 3525, 3675, 4123, 4301, 4389, 4485, 4675, 4715, 4725, 4743, 4851, 5145, 5487, 5643, 5775, 6237, 6279, 6545 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Every number of the sequence has at least three different prime factors. Also, the sequence is infinite (it contains all numbers of the form 3^a*5^b*7^c with a,b,c>0). - Emmanuel Vantieghem, Nov 21 2016

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

n = 315 = 3*3*5*7 is not a power of a prime, has 3 prime factors and (3+5)/2=7 divides n.

MAPLE

filter:= proc(n) local F;

  F:= numtheory:-factorset(n);

  nops(F) > 2 and n mod (min(F)+max(F))/2 = 0

end proc:

select(filter, [seq(i, i=1..10^4, 2)]); # Robert Israel, Nov 21 2016

MATHEMATICA

Rest@ Select[Range@ 6600, Function[n, And[IntegerQ@ #, Divisible[n, #], ! PrimePowerQ@ n] &[(#[[-1, 1]] + #[[1, 1]])/2] &@ FactorInteger@ n]] (* Michael De Vlieger, Nov 24 2016 *)

CROSSREFS

Cf. A006530, A020639, A088948, A088949.

Sequence in context: A228307 A179143 A176878 * A308643 A229094 A307108

Adjacent sequences:  A088592 A088593 A088594 * A088596 A088597 A088598

KEYWORD

nonn

AUTHOR

Labos Elemer, Nov 20 2003

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 November 20 05:07 EST 2019. Contains 329323 sequences. (Running on oeis4.)