21356778 has 8 divisors (see below), whose sum is σ = 42713568. Its totient is φ = 7118924.

The previous prime is 21356773. The next prime is 21356833. The reversal of 21356778 is 87765312.

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

21356778 is an admirable number.

It is a super-2 number, since 2×21356778² = 912223933082568, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21356773) 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, 1779726 + ... + 1779737.

It is an arithmetic number, because the mean of its divisors is an integer number (5339196).

Almost surely, 2^21356778 is an apocalyptic number.

21356778 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.

21356778 is a wasteful number, since it uses less digits than its factorization.

21356778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3559468.

The product of its digits is 70560, while the sum is 39.

The square root of 21356778 is about 4621.3394162299. The cubic root of 21356778 is about 277.4460701951.

The spelling of 21356778 in words is "twenty-one million, three hundred fifty-six thousand, seven hundred seventy-eight".