21212021891 has 2 divisors, whose sum is σ = 21212021892. Its totient is φ = 21212021890.

The previous prime is 21212021879. The next prime is 21212021911. The reversal of 21212021891 is 19812021212.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21212021891 is a prime.

It is not a weakly prime, because it can be changed into another prime (21212021801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606010945 + 10606010946.

It is an arithmetic number, because the mean of its divisors is an integer number (10606010946).

Almost surely, 2^21212021891 is an apocalyptic number.

21212021891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212021891 is an equidigital number, since it uses as much as digits as its factorization.

21212021891 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1152, while the sum is 29.

The spelling of 21212021891 in words is "twenty-one billion, two hundred twelve million, twenty-one thousand, eight hundred ninety-one".