21781226 has 4 divisors (see below), whose sum is σ = 32671842. Its totient is φ = 10890612.

The previous prime is 21781223. The next prime is 21781247. The reversal of 21781226 is 62218712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 13653025 + 8128201 = 3695^2 + 2851^2 .

It is not an unprimeable number, because it can be changed into a prime (21781223) 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 as a sum of consecutive naturals, namely, 5445305 + ... + 5445308.

Almost surely, 2^21781226 is an apocalyptic number.

21781226 is a deficient number, since it is larger than the sum of its proper divisors (10890616).

21781226 is a wasteful number, since it uses less digits than its factorization.

21781226 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10890615.

The product of its digits is 2688, while the sum is 29.

The square root of 21781226 is about 4667.0361044243. The cubic root of 21781226 is about 279.2720290594.

Adding to 21781226 its reverse (62218712), we get a palindrome (83999938).

The spelling of 21781226 in words is "twenty-one million, seven hundred eighty-one thousand, two hundred twenty-six".