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A218558 Next number that is the product of exactly three (not necessarily distinct) primes, after 10*n. 0
8, 12, 27, 42, 42, 52, 63, 75, 92, 92, 102, 114, 124, 138, 147, 153, 164, 171, 182, 195, 207, 212, 222, 231, 242, 255, 261, 273, 282, 292, 310, 316, 322, 332, 343, 354, 363, 374, 385, 399, 402, 412, 423, 434, 442, 452, 465, 474, 483, 494, 506 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
This is to "triprimes" A014612 as A185008 is to semiprimes A001358, and as A218255 is to primes A000040.
The first equal terms are a(4) = a(5) = 42. The density of numbers n such that a(n) = a(n+1) is 1. Similarly, the density of numbers n such that a(n) = a(n+1) = ... = a(n+k) is 1 for any fixed k. - Charles R Greathouse IV, Aug 30 2017
LINKS
FORMULA
a(n) = MIN[k in A014612 and k > 10*n = A008592(n)].
EXAMPLE
a(0) = 8, the first number that is the product of exactly three (not necessarily distinct) primes.
a(1) = 12 = 2^2 * 3, which is >10*1=10.
a(3) = 42 even though 30 = 2*3*5 is a "triprime" because we use ">" rather that ">=" in the definition.
PROG
(PARI) a(n)=n*=10; while(bigomega(n++)!=3, ); n \\ Charles R Greathouse IV, Aug 30 2017
CROSSREFS
Sequence in context: A006983 A283148 A072327 * A181735 A161415 A256531
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Nov 02 2012
EXTENSIONS
Offset corrected by Charles R Greathouse IV, Aug 30 2017
STATUS
approved

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Last modified July 20 14:37 EDT 2024. Contains 374446 sequences. (Running on oeis4.)