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A072997
Smallest prime p such that Product_{primes q <= p} q+1 >= n*Product_{primes q <= p} q.
2
2, 3, 13, 31, 89, 239, 617, 1571, 4007, 10141, 25673, 64853, 163367, 412007, 1037759, 2614369, 6584857, 16585291, 41764859, 105178831, 264877933, 667038311, 1679809291, 4230219377, 10652786759, 26826453991, 67555877849
OFFSET
1,1
COMMENTS
For k > 2, the primorial number A034386(A072997(k)) = A002110(A072986(k)) is the least unitary k-abundant number, i.e., the least number m such that usigma(m) >= k*m, where usigma(m) = A034448(m) is the sum of unitary divisors of m. The sequence of these primorials is the unitary version of A023199. - Amiram Eldar, Aug 24 2018
FORMULA
It seems that lim_{n -> oo} a(n+1)/a(n) exists and is > 2.
a(n) = A000040(A072986(n)). - Amiram Eldar, Aug 24 2018
MATHEMATICA
n=x=y=1; Do[x *= (Prime[s] + 1); y *= Prime[s]; If[x >= n*y, Print[Prime[s]]; n++ ], {s, 1, 10^6}] (* Ryan Propper, Jul 22 2005 *)
PROG
(PARI) a(n)=if(n<0, 0, s=1; while(prod(i=1, s, prime(i)+1)<prod(i=1, s, prime(i))*n, s++); prime(s));
CROSSREFS
Cf. A072986.
Sequence in context: A317898 A317187 A296291 * A037428 A073688 A299967
KEYWORD
hard,more,nonn
AUTHOR
Benoit Cloitre, Aug 14 2002
EXTENSIONS
7 more terms from Ryan Propper, Jul 22 2005
a(18)-a(22) added by Amiram Eldar, Aug 24 2018 from the data at A072986
a(23)-a(27) from Keith F. Lynch, Jan 13 2024
STATUS
approved