21211211999921 has 2 divisors, whose sum is σ = 21211211999922. Its totient is φ = 21211211999920.

The previous prime is 21211211999903. The next prime is 21211212000061. The reversal of 21211211999921 is 12999911211212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11264984632225 + 9946227367696 = 3356335^2 + 3153764^2 .

It is a cyclic number.

It is not a de Polignac number, because 21211211999921 - 2⁴² = 16813165488817 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21211211999921.

It is not a weakly prime, because it can be changed into another prime (21211211990921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605605999960 + 10605605999961.

It is an arithmetic number, because the mean of its divisors is an integer number (10605605999961).

Almost surely, 2^{21211211999921} is an apocalyptic number.

It is an amenable number.

21211211999921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21211211999921 is an equidigital number, since it uses as much as digits as its factorization.

21211211999921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 104976, while the sum is 50.

The spelling of 21211211999921 in words is "twenty-one trillion, two hundred eleven billion, two hundred eleven million, nine hundred ninety-nine thousand, nine hundred twenty-one".