OFFSET
1,1
COMMENTS
Corresponding values of tau(a(n)): 4, 2, 2, 2, 4, 2, 4, 2, 2, 2, 4, 2, 8, 2, 4, 2, 8, 2, 4, 2, 4, 4, 8, 2, 4, 4, 2, 2, 8, 2, ...
Triples of [tau(a(n) - 1), tau(a(n)), tau(a(n) + 1)] = [n * tau(a(n)), tau(a(n)), n * tau(a(n))]: [4, 4, 4], [4, 2, 4], [6, 2, 6], [8, 2, 8], [20, 4, 20], [12, 2, 12], [28, 4, 28], [16, 2, 16], [18, 2, 18], [20, 2, 20], ...
EXAMPLE
a(3) = 19 because 19 is the smallest number m such that tau(m-1) = tau(m+1) = 3 * tau(m); tau(18) = tau(20) = 3 * tau(19) = 3 * 2 = 6.
PROG
(Magma) Ax:=func<n|exists(r){m: m in[2..10^6] | #Divisors(m - 1) eq n * #Divisors(m) and #Divisors(m + 1) eq n * #Divisors(m)} select r else 0>; [Ax(n): n in [1..10]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jan 25 2022
EXTENSIONS
a(11)-a(16) from Jon E. Schoenfield, Jan 26 2022
More terms from Jon E. Schoenfield and David A. Corneth, Jan 27 2022
STATUS
approved