

A215659


Values of k such that k*(k  1) is a primorial number.


5




OFFSET

1,1


COMMENTS

Values of k in A215658.
See A161620 for the primorial values.  Jeppe Stig Nielsen, Mar 27 2018


LINKS

Table of n, a(n) for n=1..5.
Carol Nelson, David E. Penney and Carl Pomerance, 714 and 715, J. Recreational Math. 7:2 (1994), pp. 8789.


FORMULA

a(n) * (a(n)  1) = A215658(n)#, where p# = 2 * 3 * 5 * 7 * 11 * ... * p is a primorial, the product of the primes from 2 to p.


MATHEMATICA

Select[Range[10^5], Product[Prime@ i, {i, PrimeNu@ #}] == # &[# (#  1)] &] (* Michael De Vlieger, Apr 10 2018 *)


CROSSREFS

Cf. A215658, A161620.
Sequence in context: A014627 A145781 A109162 * A028688 A030753 A003040
Adjacent sequences: A215656 A215657 A215658 * A215660 A215661 A215662


KEYWORD

nonn,more


AUTHOR

Jonathan Sondow, Sep 07 2012


EXTENSIONS

Name improved by Jeppe Stig Nielsen, Mar 27 2018


STATUS

approved



