21009999971 has 2 divisors, whose sum is σ = 21009999972. Its totient is φ = 21009999970.

The previous prime is 21009999931. The next prime is 21010000009. The reversal of 21009999971 is 17999990012.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21009999971 is a prime.

It is not a weakly prime, because it can be changed into another prime (21009999931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504999985 + 10504999986.

It is an arithmetic number, because the mean of its divisors is an integer number (10504999986).

Almost surely, 2^21009999971 is an apocalyptic number.

21009999971 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009999971 is an equidigital number, since it uses as much as digits as its factorization.

21009999971 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 826686, while the sum is 56.

The spelling of 21009999971 in words is "twenty-one billion, nine million, nine hundred ninety-nine thousand, nine hundred seventy-one".