21515403491 has 2 divisors, whose sum is σ = 21515403492. Its totient is φ = 21515403490.

The previous prime is 21515403457. The next prime is 21515403527. The reversal of 21515403491 is 19430451512.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21515403491 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21515403431) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10757701745 + 10757701746.

It is an arithmetic number, because the mean of its divisors is an integer number (10757701746).

Almost surely, 2^21515403491 is an apocalyptic number.

21515403491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21515403491 is an equidigital number, since it uses as much as digits as its factorization.

21515403491 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 21600, while the sum is 35.

The spelling of 21515403491 in words is "twenty-one billion, five hundred fifteen million, four hundred three thousand, four hundred ninety-one".