OFFSET
1,1
COMMENTS
Pinner proves that this sequence is infinite, and in particular a(n) << n (log n)^7. The correct order is conjectured to be around n sqrt(log n). - Charles R Greathouse IV, Jul 21 2015
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Christopher G. Pinner, Repeated values of the divisor function, Quart. J. Math. Oxford Ser. (2) 48:192 (1997), pp. 499-502.
EXAMPLE
8 is a member as 10 and 6 both have 4 divisors.
MATHEMATICA
Select[ Range@ 290, DivisorSigma[0, # - 2] == DivisorSigma[0, # + 2] &] (* Robert G. Wilson v, Jul 21 2015 *)
PROG
(Magma) [ n : n in [3..300] | Denominator((NumberOfDivisors(n-2))/(NumberOfDivisors(n+2))) eq 1 and Denominator((NumberOfDivisors(n+2))/(NumberOfDivisors(n-2))) eq 1];
(PARI) is(n)=n>4&&numdiv(n-2)==numdiv(n+2) \\ Charles R Greathouse IV, Jul 21 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Jul 21 2015
STATUS
approved