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A164853 a(n) = lcm(first n semiprimes). 2
4, 12, 36, 180, 1260, 1260, 1260, 13860, 69300, 900900, 900900, 15315300, 15315300, 290990700, 290990700, 6692786100, 46849502700, 46849502700, 46849502700, 46849502700, 1358635578300, 42117702927300, 42117702927300, 42117702927300 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is to A002110 Primorial numbers as semiprimes A001358 is to prime A000040.

a(n) = a(n-1) if A001358(n) is the product of two distinct odd primes. - Robert Israel, Feb 05 2020

LINKS

Robert Israel, Table of n, a(n) for n = 1..1266

FORMULA

a(n) = lcm_{i=1..n} A001358(i).

a(1) = A001358(1) = 4; a(n) = lcm(a(n-1), A001358(n)). - Zak Seidov, Aug 31 2009

EXAMPLE

a(1) = 4, the first semiprime. a(2) = lcm(4,6) = 12. a(3) = lcm(4,6,9) = 36.

MAPLE

N:= 10^3: # to use semiprimes <= N

SP:= select(t -> numtheory:-bigomega(t)=2, [$4..N]):

A[1]:= SP[1]:

for n from 2 to N do

A[n]:= ilcm(A[n-1], SP[n])

od:

seq(A[i], i=1..N); # Robert Israel, Feb 05 2020

MATHEMATICA

With[{s=Select[Range[100], PrimeOmega[#]==2&]}, Table[LCM@@Take[s, n], {n, Length[s]}]] (* Harvey P. Dale, May 05 2015 *)

CROSSREFS

Cf. A001358, A002110.

Sequence in context: A293857 A052643 A140123 * A076124 A247952 A183923

Adjacent sequences:  A164850 A164851 A164852 * A164854 A164855 A164856

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Aug 28 2009

EXTENSIONS

More terms from Zak Seidov, Aug 31 2009

STATUS

approved

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Last modified August 13 19:30 EDT 2020. Contains 336451 sequences. (Running on oeis4.)