21538100 has 18 divisors (see below), whose sum is σ = 46737894. Its totient is φ = 8615200.

The previous prime is 21538091. The next prime is 21538109. The reversal of 21538100 is 183512.

It is an interprime number because it is at equal distance from previous prime (21538091) and next prime (21538109).

It can be written as a sum of positive squares in 3 ways, for example, as 119716 + 21418384 = 346^2 + 4628^2 .

It is a super-2 number, since 2×21538100² = 927779503220000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21538109) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 107591 + ... + 107790.

Almost surely, 2^21538100 is an apocalyptic number.

21538100 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21538100 is an abundant number, since it is smaller than the sum of its proper divisors (25199794).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21538100 is a wasteful number, since it uses less digits than its factorization.

21538100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 215395 (or 215388 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 21538100 is about 4640.9158578884. The cubic root of 21538100 is about 278.2290436809.

The spelling of 21538100 in words is "twenty-one million, five hundred thirty-eight thousand, one hundred".