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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A115403 Numbers n such that n^3+1 is 3-almost prime (product of three primes). 3
3, 9, 10, 12, 13, 21, 25, 30, 34, 36, 40, 46, 52, 66, 76, 81, 90, 96, 118, 120, 126, 130, 132, 142, 144, 154, 165, 168, 172, 177, 180, 193, 196, 198, 204, 216, 226, 228, 238, 240, 246, 250, 256, 262, 268, 273, 282, 288, 294, 312, 333, 336, 345, 346, 366, 370 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It appears that there is only one known example of three consecutive primes p, q, r whose product is 1 more than a perfect cube, namely 7*11*13 = 1001 and that probably no other examples exist. - N. J. A. Sloane, Apr 27 2008

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

n^3+1=p*q*r where p, q, r are primes (not necessarily distinct).

EXAMPLE

9 is a member because 9^3+1=730=2*5*73 (product of three primes).

PROG

(PARI) isok(n) = bigomega(n^3+1) == 3; \\ Michel Marcus, Oct 10 2013

CROSSREFS

Cf. A001093, A014612 (3-almost primes).

Sequence in context: A309349 A024574 A119203 * A282409 A059012 A055063

Adjacent sequences:  A115400 A115401 A115402 * A115404 A115405 A115406

KEYWORD

nonn

AUTHOR

Zak Seidov, Mar 08 2006

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 October 21 08:16 EDT 2019. Contains 328292 sequences. (Running on oeis4.)