21356890 has 8 divisors (see below), whose sum is σ = 38442420. Its totient is φ = 8542752.

The previous prime is 21356873. The next prime is 21356891. The reversal of 21356890 is 9865312.

It can be written as a sum of positive squares in 2 ways, for example, as 21353641 + 3249 = 4621^2 + 57^2 .

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

It is a super-2 number, since 2×21356890² = 912233500944200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21356891) 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, 1067835 + ... + 1067854.

Almost surely, 2^21356890 is an apocalyptic number.

21356890 is a deficient number, since it is larger than the sum of its proper divisors (17085530).

21356890 is a wasteful number, since it uses less digits than its factorization.

21356890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2135696.

The product of its (nonzero) digits is 12960, while the sum is 34.

The square root of 21356890 is about 4621.3515339130. The cubic root of 21356890 is about 277.4465551919.

It can be divided in two parts, 2135 and 6890, that added together give a square (9025 = 95²).

The spelling of 21356890 in words is "twenty-one million, three hundred fifty-six thousand, eight hundred ninety".