21666014661566 has 16 divisors (see below), whose sum is σ = 35515786955760. Its totient is φ = 9830880588480.

The previous prime is 21666014661547. The next prime is 21666014661587. The reversal of 21666014661566 is 66516641066612.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 865381901 + ... + 865406936.

It is an arithmetic number, because the mean of its divisors is an integer number (2219736684735).

Almost surely, 2^{21666014661566} is an apocalyptic number.

21666014661566 is a deficient number, since it is larger than the sum of its proper divisors (13849772294194).

21666014661566 is a wasteful number, since it uses less digits than its factorization.

21666014661566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1730789419.

The product of its (nonzero) digits is 11197440, while the sum is 56.

The spelling of 21666014661566 in words is "twenty-one trillion, six hundred sixty-six billion, fourteen million, six hundred sixty-one thousand, five hundred sixty-six".