21357988 has 6 divisors (see below), whose sum is σ = 37376486. Its totient is φ = 10678992.

The previous prime is 21357983. The next prime is 21357997. The reversal of 21357988 is 88975312.

It can be written as a sum of positive squares in only one way, i.e., 11573604 + 9784384 = 3402^2 + 3128^2 .

It is not an unprimeable number, because it can be changed into a prime (21357983) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2669745 + ... + 2669752.

Almost surely, 2^21357988 is an apocalyptic number.

It is an amenable number.

21357988 is a deficient number, since it is larger than the sum of its proper divisors (16018498).

21357988 is a wasteful number, since it uses less digits than its factorization.

21357988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5339501 (or 5339499 counting only the distinct ones).

The product of its digits is 120960, while the sum is 43.

The square root of 21357988 is about 4621.4703288023. The cubic root of 21357988 is about 277.4513098027.

The spelling of 21357988 in words is "twenty-one million, three hundred fifty-seven thousand, nine hundred eighty-eight".