21290818 has 4 divisors (see below), whose sum is σ = 31936230. Its totient is φ = 10645408.

The previous prime is 21290813. The next prime is 21290839. The reversal of 21290818 is 81809212.

It is a happy number.

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

It can be written as a sum of positive squares in only one way, i.e., 12723489 + 8567329 = 3567^2 + 2927^2 .

It is a super-2 number, since 2×21290818² = 906597862218248, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 21290818.

It is not an unprimeable number, because it can be changed into a prime (21290813) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5322703 + ... + 5322706.

Almost surely, 2^21290818 is an apocalyptic number.

21290818 is a deficient number, since it is larger than the sum of its proper divisors (10645412).

21290818 is a wasteful number, since it uses less digits than its factorization.

21290818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10645411.

The product of its (nonzero) digits is 2304, while the sum is 31.

The square root of 21290818 is about 4614.1974383418. The cubic root of 21290818 is about 277.1601466776.

The spelling of 21290818 in words is "twenty-one million, two hundred ninety thousand, eight hundred eighteen".