21005100 has 54 divisors (see below), whose sum is σ = 65842140. Its totient is φ = 5601120.

The previous prime is 21005087. The next prime is 21005111. The reversal of 21005100 is 150012.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 10770 + ... + 12569.

Almost surely, 2^21005100 is an apocalyptic number.

21005100 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21005100 is an abundant number, since it is smaller than the sum of its proper divisors (44837040).

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

21005100 is a wasteful number, since it uses less digits than its factorization.

21005100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23359 (or 23349 counting only the distinct ones).

The product of its (nonzero) digits is 10, while the sum is 9.

The square root of 21005100 is about 4583.1321167952. The cubic root of 21005100 is about 275.9147499784.

Adding to 21005100 its reverse (150012), we get a palindrome (21155112).

The spelling of 21005100 in words is "twenty-one million, five thousand, one hundred".