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

 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 Harvey P. Dale, Table of n, a(n) for n = 1..1000 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 Cf. A000217, A068443, A119663, A121478. Sequence in context: A358988 A254466 A235304 * A235921 A236432 A118279 Adjacent sequences: A121476 A121477 A121478 * A121480 A121481 A121482 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.

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