21087818 has 4 divisors (see below), whose sum is σ = 31631730. Its totient is φ = 10543908.

The previous prime is 21087809. The next prime is 21087827. The reversal of 21087818 is 81878012.

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

It is an interprime number because it is at equal distance from previous prime (21087809) and next prime (21087827).

It can be written as a sum of positive squares in only one way, i.e., 10738729 + 10349089 = 3277^2 + 3217^2 .

It is a super-2 number, since 2×21087818² = 889392136002248, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5271953 + ... + 5271956.

Almost surely, 2^21087818 is an apocalyptic number.

21087818 is a deficient number, since it is larger than the sum of its proper divisors (10543912).

21087818 is a wasteful number, since it uses less digits than its factorization.

21087818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10543911.

The product of its (nonzero) digits is 7168, while the sum is 35.

The square root of 21087818 is about 4592.1474279470. The cubic root of 21087818 is about 276.2764593180.

The spelling of 21087818 in words is "twenty-one million, eighty-seven thousand, eight hundred eighteen".