21157121064 has 32 divisors (see below), whose sum is σ = 54018184320. Its totient is φ = 6902322816.

The previous prime is 21157121057. The next prime is 21157121099. The reversal of 21157121064 is 46012175112.

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, 9377029 + ... + 9379284.

It is an arithmetic number, because the mean of its divisors is an integer number (1688068260).

Almost surely, 2^21157121064 is an apocalyptic number.

21157121064 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21157121064 is an abundant number, since it is smaller than the sum of its proper divisors (32861063256).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21157121064 is a wasteful number, since it uses less digits than its factorization.

21157121064 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18756369 (or 18756365 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 30.

Adding to 21157121064 its reverse (46012175112), we get a palindrome (67169296176).

The spelling of 21157121064 in words is "twenty-one billion, one hundred fifty-seven million, one hundred twenty-one thousand, sixty-four".