21356691 has 4 divisors (see below), whose sum is σ = 28475592. Its totient is φ = 14237792.

The previous prime is 21356689. The next prime is 21356711. The reversal of 21356691 is 19665312.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21356691 - 2¹ = 21356689 is a prime.

It is a super-2 number, since 2×21356691² = 912216500938962, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21356611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3559446 + ... + 3559451.

It is an arithmetic number, because the mean of its divisors is an integer number (7118898).

Almost surely, 2^21356691 is an apocalyptic number.

21356691 is a deficient number, since it is larger than the sum of its proper divisors (7118901).

21356691 is an equidigital number, since it uses as much as digits as its factorization.

21356691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7118900.

The product of its digits is 9720, while the sum is 33.

The square root of 21356691 is about 4621.3300033648. The cubic root of 21356691 is about 277.4456934554.

The spelling of 21356691 in words is "twenty-one million, three hundred fifty-six thousand, six hundred ninety-one".