21919778 has 4 divisors (see below), whose sum is σ = 32879670. Its totient is φ = 10959888.

The previous prime is 21919771. The next prime is 21919811. The reversal of 21919778 is 87791912.

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., 12229009 + 9690769 = 3497^2 + 3113^2 .

It is not an unprimeable number, because it can be changed into a prime (21919771) 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 as a sum of consecutive naturals, namely, 5479943 + ... + 5479946.

Almost surely, 2^21919778 is an apocalyptic number.

21919778 is a deficient number, since it is larger than the sum of its proper divisors (10959892).

21919778 is a wasteful number, since it uses less digits than its factorization.

21919778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10959891.

The product of its digits is 63504, while the sum is 44.

The square root of 21919778 is about 4681.8562558028. The cubic root of 21919778 is about 279.8629346155.

The spelling of 21919778 in words is "twenty-one million, nine hundred nineteen thousand, seven hundred seventy-eight".