OFFSET
1,1
COMMENTS
A subsequence of A011257.
If 3^{k+1}-1 = d*D such that p = 2*b^{k+1}*(d+1) - 1 and q = 2*(b^{k+1}+D)-1 are distinct primes, then n = 3^k*p*q is a term of this sequence.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[506*10^4], DivisorSigma[1, #]/EulerPhi[#]==9/4&] (* Harvey P. Dale, Jun 22 2019 *)
PROG
(PARI) for( n=1, 1e7, sigma(n)==9/4*eulerphi(n) && print1(n", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Aug 22 2009
STATUS
approved