OFFSET
1,2
COMMENTS
For n in {1,2,3,4,6}, n = d(prime(n)-1). There are no others with this property, as conjectured by Raphie Frank and proved by Charles R Greathouse IV on Physics Forums (Nov, 2010).
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
Physics Forums, Prime Indices & the Divisors of (p'_n - 1): A Lattice-Related Question , Nov 2010
EXAMPLE
d(701 - 1)*7 = pi(701) = 126. The 126th prime is 701 and d(701 - 1) = 18; 18 divides 126 (7 times), so 126 is a member of this sequence.
MATHEMATICA
Select[Range[352], Mod[#, DivisorSigma[0, Prime[#] - 1]] == 0 &] (* T. D. Noe, Oct 11 2012 *)
PROG
(PARI) is(n)=n%numdiv(prime(n)-1)==0 \\ Charles R Greathouse IV, Oct 09 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Raphie Frank, Oct 04 2012
EXTENSIONS
a(12), a(31), a(39) from Charles R Greathouse IV, Oct 09 2012
STATUS
approved