21780421 has 8 divisors (see below), whose sum is σ = 24265080. Its totient is φ = 19411392.

The previous prime is 21780377. The next prime is 21780431. The reversal of 21780421 is 12408712.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 260100 + 21520321 = 510^2 + 4639^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21780421 - 2¹³ = 21772229 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21780431) 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, 28510 + ... + 29263.

It is an arithmetic number, because the mean of its divisors is an integer number (3033135).

Almost surely, 2^21780421 is an apocalyptic number.

It is an amenable number.

21780421 is a deficient number, since it is larger than the sum of its proper divisors (2484659).

21780421 is a wasteful number, since it uses less digits than its factorization.

21780421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57815.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21780421 is about 4666.9498604549. The cubic root of 21780421 is about 279.2685885314.

It can be divided in two parts, 21780 and 421, that added together give a square (22201 = 149²).

The spelling of 21780421 in words is "twenty-one million, seven hundred eighty thousand, four hundred twenty-one".