21491567 has 2 divisors, whose sum is σ = 21491568. Its totient is φ = 21491566.

The previous prime is 21491563. The next prime is 21491579. The reversal of 21491567 is 76519412.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21491567 - 2² = 21491563 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21491563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10745783 + 10745784.

It is an arithmetic number, because the mean of its divisors is an integer number (10745784).

Almost surely, 2^21491567 is an apocalyptic number.

21491567 is a deficient number, since it is larger than the sum of its proper divisors (1).

21491567 is an equidigital number, since it uses as much as digits as its factorization.

21491567 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15120, while the sum is 35.

The square root of 21491567 is about 4635.8998047844. The cubic root of 21491567 is about 278.0285282043.

The spelling of 21491567 in words is "twenty-one million, four hundred ninety-one thousand, five hundred sixty-seven".