21781254 has 16 divisors (see below), whose sum is σ = 47522880. Its totient is φ = 6600360.

The previous prime is 21781247. The next prime is 21781259. The reversal of 21781254 is 45218712.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21781259) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 164944 + ... + 165075.

It is an arithmetic number, because the mean of its divisors is an integer number (2970180).

Almost surely, 2^21781254 is an apocalyptic number.

21781254 is an abundant number, since it is smaller than the sum of its proper divisors (25741626).

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

21781254 is a wasteful number, since it uses less digits than its factorization.

21781254 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 330035.

The product of its digits is 4480, while the sum is 30.

The square root of 21781254 is about 4667.0391041859. The cubic root of 21781254 is about 279.2721487284.

Adding to 21781254 its reverse (45218712), we get a palindrome (66999966).

The spelling of 21781254 in words is "twenty-one million, seven hundred eighty-one thousand, two hundred fifty-four".