OFFSET
1,1
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
10 is a term since both 10 and 2*10+1=21 have 4 divisors: {1,2,5,10} and {1,3,7,21}.
MATHEMATICA
Select[Range[400], CompositeQ[#] && DivisorSigma[0, #] == DivisorSigma[0, 2*#+1] &] (* Amiram Eldar, Feb 18 2020 *)
PROG
(PARI) isok(n) = !isprime(n) && (numdiv(n) == numdiv(2*n+1)); \\ Michel Marcus, Oct 10 2013
(Magma) [k:k in [2..400]| not IsPrime(k) and #Divisors(k) eq #Divisors(2*k+1)]; // Marius A. Burtea, Feb 18 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Aug 03 2006
STATUS
approved