21001998427 has 2 divisors, whose sum is σ = 21001998428. Its totient is φ = 21001998426.

The previous prime is 21001998397. The next prime is 21001998443. The reversal of 21001998427 is 72489910012.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21001998427 - 2⁷ = 21001998299 is a prime.

It is not a weakly prime, because it can be changed into another prime (21001998527) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500999213 + 10500999214.

It is an arithmetic number, because the mean of its divisors is an integer number (10500999214).

Almost surely, 2^21001998427 is an apocalyptic number.

21001998427 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001998427 is an equidigital number, since it uses as much as digits as its factorization.

21001998427 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 72576, while the sum is 43.

The spelling of 21001998427 in words is "twenty-one billion, one million, nine hundred ninety-eight thousand, four hundred twenty-seven".