The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A121479 Triangular numbers with more than three distinct prime factors. 3
210, 630, 780, 990, 1326, 1540, 1596, 1770, 1830, 2145, 2346, 2415, 2850, 2926, 3003, 3486, 3570, 3828, 4095, 4186, 4278, 4560, 4950, 5460, 5565, 6105, 6216, 6555, 6670, 6786, 7140, 7260, 7626, 8385, 8646, 8778, 9180, 9730, 9870, 10296, 10440, 10878 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
20*21/2 = 2*3*5*7 = 210 is the smalles triangular number with more than three distinct prime factors, hence a(1) = 210.
MATHEMATICA
Select[Accumulate[Range[200]], PrimeNu[#]>3&] (* Harvey P. Dale, Jun 06 2013 *)
PROG
(PARI) for(n=1, 100, k=binomial(n+1, 2); if(omega(k)>3, print1(k, ", ")))
CROSSREFS
Sequence in context: A358988 A254466 A235304 * A235921 A236432 A118279
KEYWORD
easy,nonn
AUTHOR
Klaus Brockhaus, Aug 01 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 26 05:37 EDT 2024. Contains 372807 sequences. (Running on oeis4.)