21487691 has 4 divisors (see below), whose sum is σ = 21600384. Its totient is φ = 21375000.

The previous prime is 21487673. The next prime is 21487693. The reversal of 21487691 is 19678412.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21487691 is a prime.

It is a super-2 number, since 2×21487691² = 923441729022962, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21487693) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 56060 + ... + 56441.

It is an arithmetic number, because the mean of its divisors is an integer number (5400096).

Almost surely, 2^21487691 is an apocalyptic number.

21487691 is a deficient number, since it is larger than the sum of its proper divisors (112693).

21487691 is a wasteful number, since it uses less digits than its factorization.

21487691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 112692.

The product of its digits is 24192, while the sum is 38.

The square root of 21487691 is about 4635.4817441125. The cubic root of 21487691 is about 278.0118130687.

The spelling of 21487691 in words is "twenty-one million, four hundred eighty-seven thousand, six hundred ninety-one".