21219778 has 4 divisors (see below), whose sum is σ = 31829670. Its totient is φ = 10609888.

The previous prime is 21219767. The next prime is 21219787. The reversal of 21219778 is 87791212.

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., 17918289 + 3301489 = 4233^2 + 1817^2 .

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 5304943 + ... + 5304946.

Almost surely, 2^21219778 is an apocalyptic number.

21219778 is a deficient number, since it is larger than the sum of its proper divisors (10609892).

21219778 is a wasteful number, since it uses less digits than its factorization.

21219778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10609891.

The product of its digits is 14112, while the sum is 37.

The square root of 21219778 is about 4606.4930261534. The cubic root of 21219778 is about 276.8515410861.

The spelling of 21219778 in words is "twenty-one million, two hundred nineteen thousand, seven hundred seventy-eight".