21538945391 has 2 divisors, whose sum is σ = 21538945392. Its totient is φ = 21538945390.

The previous prime is 21538945369. The next prime is 21538945403. The reversal of 21538945391 is 19354983512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21538945391 - 2¹⁴ = 21538929007 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21538945301) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10769472695 + 10769472696.

It is an arithmetic number, because the mean of its divisors is an integer number (10769472696).

Almost surely, 2^21538945391 is an apocalyptic number.

21538945391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21538945391 is an equidigital number, since it uses as much as digits as its factorization.

21538945391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1166400, while the sum is 50.

The spelling of 21538945391 in words is "twenty-one billion, five hundred thirty-eight million, nine hundred forty-five thousand, three hundred ninety-one".