OFFSET
1,1
COMMENTS
a(n) is even. If a(n) is odd then two consecutive numbers are perfect squares. This only happens with (0, 1) which does not give terms. - David A. Corneth, Aug 16 2021
EXAMPLE
tau(89484) = tau(89483) + tau(89485); 12 = 4 + 8.
sigma(89484) = sigma(89483) + sigma(89485); 208824 = 91608 + 117216.
MATHEMATICA
Select[Range[200000], DivisorSigma[{0, 1}, # - 1] + DivisorSigma[{0, 1}, # + 1] - DivisorSigma[{0, 1}, # ] == {0, 0} &] (* Amiram Eldar, Aug 16 2021 *)
PROG
(Magma) [m: m in [2..10^5] | #Divisors(m) eq #Divisors(m - 1) + #Divisors(m + 1) and &+Divisors(m) eq &+Divisors(m - 1) + &+Divisors(m + 1)]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jaroslav Krizek, Aug 15 2021
EXTENSIONS
a(14)-a(15) from Martin Ehrenstein, Sep 24 2021
STATUS
approved