21009990477491 has 2 divisors, whose sum is σ = 21009990477492. Its totient is φ = 21009990477490.

The previous prime is 21009990477473. The next prime is 21009990477521. The reversal of 21009990477491 is 19477409990012.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21009990477491 is a prime.

It is not a weakly prime, because it can be changed into another prime (21009990477691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504995238745 + 10504995238746.

It is an arithmetic number, because the mean of its divisors is an integer number (10504995238746).

Almost surely, 2^{21009990477491} is an apocalyptic number.

21009990477491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009990477491 is an equidigital number, since it uses as much as digits as its factorization.

21009990477491 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10287648, while the sum is 62.

The spelling of 21009990477491 in words is "twenty-one trillion, nine billion, nine hundred ninety million, four hundred seventy-seven thousand, four hundred ninety-one".