21000400123 has 16 divisors (see below), whose sum is σ = 22204235520. Its totient is φ = 19806594336.

The previous prime is 21000400111. The next prime is 21000400129. The reversal of 21000400123 is 32100400012.

It is a cyclic number.

It is not a de Polignac number, because 21000400123 - 2¹³ = 21000391931 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21000400129) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5918836 + ... + 5922382.

It is an arithmetic number, because the mean of its divisors is an integer number (1387764720).

Almost surely, 2^21000400123 is an apocalyptic number.

21000400123 is a deficient number, since it is larger than the sum of its proper divisors (1203835397).

21000400123 is a wasteful number, since it uses less digits than its factorization.

21000400123 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4866.

The product of its (nonzero) digits is 48, while the sum is 13.

Adding to 21000400123 its reverse (32100400012), we get a palindrome (53100800135).

The spelling of 21000400123 in words is "twenty-one billion, four hundred thousand, one hundred twenty-three".