21211220021 has 2 divisors, whose sum is σ = 21211220022. Its totient is φ = 21211220020.

The previous prime is 21211219973. The next prime is 21211220039. The reversal of 21211220021 is 12002211212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16374017521 + 4837202500 = 127961^2 + 69550^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21211220021 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21211219978 and 21211220005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21211210021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605610010 + 10605610011.

It is an arithmetic number, because the mean of its divisors is an integer number (10605610011).

Almost surely, 2^21211220021 is an apocalyptic number.

It is an amenable number.

21211220021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21211220021 is an equidigital number, since it uses as much as digits as its factorization.

21211220021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32, while the sum is 14.

Adding to 21211220021 its reverse (12002211212), we get a palindrome (33213431233).

The spelling of 21211220021 in words is "twenty-one billion, two hundred eleven million, two hundred twenty thousand, twenty-one".