21691266 has 8 divisors (see below), whose sum is σ = 43382544. Its totient is φ = 7230420.

The previous prime is 21691253. The next prime is 21691273. The reversal of 21691266 is 66219612.

It is a sphenic number, since it is the product of 3 distinct primes.

21691266 is an admirable number.

It is a super-2 number, since 2×21691266² = 941022041365512, which contains 22 as substring.

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1807600 + ... + 1807611.

It is an arithmetic number, because the mean of its divisors is an integer number (5422818).

Almost surely, 2^21691266 is an apocalyptic number.

21691266 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21691266 is a wasteful number, since it uses less digits than its factorization.

21691266 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3615216.

The product of its digits is 7776, while the sum is 33.

The square root of 21691266 is about 4657.3883239429. The cubic root of 21691266 is about 278.8870189119.

The spelling of 21691266 in words is "twenty-one million, six hundred ninety-one thousand, two hundred sixty-six".