21205472987 has 2 divisors, whose sum is σ = 21205472988. Its totient is φ = 21205472986.

The previous prime is 21205472969. The next prime is 21205472993. The reversal of 21205472987 is 78927450212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21205472987 - 2²⁶ = 21138364123 is a prime.

It is not a weakly prime, because it can be changed into another prime (21205472927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602736493 + 10602736494.

It is an arithmetic number, because the mean of its divisors is an integer number (10602736494).

Almost surely, 2^21205472987 is an apocalyptic number.

21205472987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205472987 is an equidigital number, since it uses as much as digits as its factorization.

21205472987 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 564480, while the sum is 47.

The spelling of 21205472987 in words is "twenty-one billion, two hundred five million, four hundred seventy-two thousand, nine hundred eighty-seven".