OFFSET
1,3
COMMENTS
The terms of A070198, and duplicates removed.
From Daniel Forgues, Apr 27 2014: (Start)
Factorizations:
5, 11, 59, 419, 839 are primes;
2519 = 11*229, 27719 = 53*523, 360359 = 173*2083,
720719 = 31*67*347, 12252239 = 29*647*653;
232792559, 5354228879 are primes;
26771144399 = 47*12907*44131, 80313433199 = 29*61*45400471;
2329089562799 is prime;
72201776446799 = 37*149*239*1091*50227;
144403552893599 is prime;
Very likely contains an infinite number of primes (see A057824). (End)
A more natural (compare with A051452) name for the sequence: lcm(1, ..., k) - 1, where k is the n-th prime power A000961(n). - Daniel Forgues, May 09 2014
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..250
PROG
(Haskell)
import Data.List (nub)
a208768 n = a208768_list !! (n-1)
a208768_list = nub a070198_list
(Python)
from math import prod
from sympy import primepi, integer_nthroot, integer_log, primerange
def A208768(n):
def f(x): return int(n+x-1-sum(primepi(integer_nthroot(x, k)[0]) for k in range(1, x.bit_length())))
m, k = n, f(n)
while m != k:
m, k = k, f(k)
return prod(p**integer_log(m, p)[0] for p in primerange(m+1))-1 # Chai Wah Wu, Aug 15 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Mar 01 2012
STATUS
approved