21491289 has 12 divisors (see below), whose sum is σ = 31090176. Its totient is φ = 14305752.

The previous prime is 21491287. The next prime is 21491297. The reversal of 21491289 is 98219412.

It is not a de Polignac number, because 21491289 - 2¹ = 21491287 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21491287) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6384 + ... + 9150.

It is an arithmetic number, because the mean of its divisors is an integer number (2590848).

Almost surely, 2^21491289 is an apocalyptic number.

It is an amenable number.

21491289 is a deficient number, since it is larger than the sum of its proper divisors (9598887).

21491289 is a wasteful number, since it uses less digits than its factorization.

21491289 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3636 (or 3633 counting only the distinct ones).

The product of its digits is 10368, while the sum is 36.

The square root of 21491289 is about 4635.8698212957. The cubic root of 21491289 is about 278.0273294044.

The spelling of 21491289 in words is "twenty-one million, four hundred ninety-one thousand, two hundred eighty-nine".