21355988 has 6 divisors (see below), whose sum is σ = 37372986. Its totient is φ = 10677992.

The previous prime is 21355987. The next prime is 21356003. The reversal of 21355988 is 88955312.

It can be written as a sum of positive squares in only one way, i.e., 16418704 + 4937284 = 4052^2 + 2222^2 .

It is a super-2 number, since 2×21355988² = 912156446912288, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21355987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2669495 + ... + 2669502.

It is an arithmetic number, because the mean of its divisors is an integer number (6228831).

Almost surely, 2^21355988 is an apocalyptic number.

It is an amenable number.

21355988 is a deficient number, since it is larger than the sum of its proper divisors (16016998).

21355988 is a wasteful number, since it uses less digits than its factorization.

21355988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5339001 (or 5338999 counting only the distinct ones).

The product of its digits is 86400, while the sum is 41.

The square root of 21355988 is about 4621.2539423840. The cubic root of 21355988 is about 277.4426491876.

The spelling of 21355988 in words is "twenty-one million, three hundred fifty-five thousand, nine hundred eighty-eight".