21666124651 has 4 divisors (see below), whose sum is σ = 21666620592. Its totient is φ = 21665628712.

The previous prime is 21666124639. The next prime is 21666124673. The reversal of 21666124651 is 15642166612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21666124651 - 2¹⁵ = 21666091883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21666124621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 175351 + ... + 272176.

It is an arithmetic number, because the mean of its divisors is an integer number (5416655148).

Almost surely, 2^21666124651 is an apocalyptic number.

21666124651 is a deficient number, since it is larger than the sum of its proper divisors (495941).

21666124651 is an equidigital number, since it uses as much as digits as its factorization.

21666124651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 495940.

The product of its digits is 103680, while the sum is 40.

The spelling of 21666124651 in words is "twenty-one billion, six hundred sixty-six million, one hundred twenty-four thousand, six hundred fifty-one".