21780100 has 36 divisors (see below), whose sum is σ = 47473524. Its totient is φ = 8673280.

The previous prime is 21780097. The next prime is 21780127. The reversal of 21780100 is 108712.

It can be written as a sum of positive squares in 6 ways, for example, as 4937284 + 16842816 = 2222^2 + 4104^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 34992 + ... + 35608.

It is an arithmetic number, because the mean of its divisors is an integer number (1318709).

Almost surely, 2^21780100 is an apocalyptic number.

21780100 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21780100 is an abundant number, since it is smaller than the sum of its proper divisors (25693424).

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

21780100 is a wasteful number, since it uses less digits than its factorization.

21780100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 984 (or 977 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 19.

The square root of 21780100 is about 4666.9154695580. The cubic root of 21780100 is about 279.2672165705.

Adding to 21780100 its reverse (108712), we get a palindrome (21888812).

The spelling of 21780100 in words is "twenty-one million, seven hundred eighty thousand, one hundred".