21678777 has 12 divisors (see below), whose sum is σ = 31424484. Its totient is φ = 14401440.

The previous prime is 21678763. The next prime is 21678779. The reversal of 21678777 is 77787612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 20466576 + 1212201 = 4524^2 + 1101^2 .

It is not a de Polignac number, because 21678777 - 2¹⁴ = 21662393 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21678779) 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 11 ways as a sum of consecutive naturals, for example, 1474 + ... + 6747.

It is an arithmetic number, because the mean of its divisors is an integer number (2618707).

Almost surely, 2^21678777 is an apocalyptic number.

It is an amenable number.

21678777 is a deficient number, since it is larger than the sum of its proper divisors (9745707).

21678777 is a wasteful number, since it uses less digits than its factorization.

21678777 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8520 (or 8517 counting only the distinct ones).

The product of its digits is 230496, while the sum is 45.

The square root of 21678777 is about 4656.0473580066. The cubic root of 21678777 is about 278.8334844823.

The spelling of 21678777 in words is "twenty-one million, six hundred seventy-eight thousand, seven hundred seventy-seven".