21201220981 has 2 divisors, whose sum is σ = 21201220982. Its totient is φ = 21201220980.

The previous prime is 21201220969. The next prime is 21201221021. The reversal of 21201220981 is 18902210212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15409249956 + 5791971025 = 124134^2 + 76105^2 .

It is a cyclic number.

It is not a de Polignac number, because 21201220981 - 2⁵ = 21201220949 is a prime.

It is a super-2 number, since 2×21201220981² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21201220921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10600610490 + 10600610491.

It is an arithmetic number, because the mean of its divisors is an integer number (10600610491).

Almost surely, 2^21201220981 is an apocalyptic number.

It is an amenable number.

21201220981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21201220981 is an equidigital number, since it uses as much as digits as its factorization.

21201220981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1152, while the sum is 28.

The spelling of 21201220981 in words is "twenty-one billion, two hundred one million, two hundred twenty thousand, nine hundred eighty-one".