21666123157 has 4 divisors (see below), whose sum is σ = 24761283616. Its totient is φ = 18570962700.

The previous prime is 21666123113. The next prime is 21666123173. The reversal of 21666123157 is 75132166612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21666123157 - 2⁷ = 21666123029 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666123197) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1547580219 + ... + 1547580232.

It is an arithmetic number, because the mean of its divisors is an integer number (6190320904).

Almost surely, 2^21666123157 is an apocalyptic number.

It is an amenable number.

21666123157 is a deficient number, since it is larger than the sum of its proper divisors (3095160459).

21666123157 is an equidigital number, since it uses as much as digits as its factorization.

21666123157 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3095160458.

The product of its digits is 90720, while the sum is 40.

Adding to 21666123157 its reverse (75132166612), we get a palindrome (96798289769).

The spelling of 21666123157 in words is "twenty-one billion, six hundred sixty-six million, one hundred twenty-three thousand, one hundred fifty-seven".