21780125 has 8 divisors (see below), whose sum is σ = 27181752. Its totient is φ = 17424000.

The previous prime is 21780097. The next prime is 21780127. The reversal of 21780125 is 52108712.

It can be written as a sum of positive squares in 4 ways, for example, as 120409 + 21659716 = 347^2 + 4654^2 .

It is not a de Polignac number, because 21780125 - 2¹⁴ = 21763741 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21780094 and 21780103.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21780127) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 86996 + ... + 87245.

It is an arithmetic number, because the mean of its divisors is an integer number (3397719).

Almost surely, 2^21780125 is an apocalyptic number.

21780125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21780125 is a deficient number, since it is larger than the sum of its proper divisors (5401627).

21780125 is an equidigital number, since it uses as much as digits as its factorization.

21780125 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 174256 (or 174246 counting only the distinct ones).

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21780125 is about 4666.9181479859. The cubic root of 21780125 is about 279.2673234215.

Adding to 21780125 its reverse (52108712), we get a palindrome (73888837).

It can be divided in two parts, 21780 and 125, that multiplied together give a square (2722500 = 1650²).

The spelling of 21780125 in words is "twenty-one million, seven hundred eighty thousand, one hundred twenty-five".