21909521654987 has 2 divisors, whose sum is σ = 21909521654988. Its totient is φ = 21909521654986.

The previous prime is 21909521654981. The next prime is 21909521655001. The reversal of 21909521654987 is 78945612590912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21909521654987 - 2¹⁶ = 21909521589451 is a prime.

It is not a weakly prime, because it can be changed into another prime (21909521654981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10954760827493 + 10954760827494.

It is an arithmetic number, because the mean of its divisors is an integer number (10954760827494).

Almost surely, 2^{21909521654987} is an apocalyptic number.

21909521654987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21909521654987 is an equidigital number, since it uses as much as digits as its factorization.

21909521654987 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 97977600, while the sum is 68.

The spelling of 21909521654987 in words is "twenty-one trillion, nine hundred nine billion, five hundred twenty-one million, six hundred fifty-four thousand, nine hundred eighty-seven".