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A072997 Smallest prime p such that Product_{primes q <= p} q+1 >= n*Product_{primes q <= p} q. 1
2, 3, 13, 31, 89, 239, 617, 1571, 4007, 10141, 25673, 64853, 163367, 412007, 1037759, 2614369, 6584857, 16585291, 41764859, 105178831, 264877933, 667038311 (list; graph; refs; listen; history; text; internal format)
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

LINKS

Table of n, a(n) for n=1..22.

FORMULA

It seems that lim_{n -> infinity} 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

Adjacent sequences:  A072994 A072995 A072996 * A072998 A072999 A073000

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

STATUS

approved

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Last modified April 13 06:02 EDT 2021. Contains 342935 sequences. (Running on oeis4.)