21154778 has 16 divisors (see below), whose sum is σ = 32348160. Its totient is φ = 10374000.

The previous prime is 21154759. The next prime is 21154789. The reversal of 21154778 is 87745112.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 29828 + ... + 30528.

It is an arithmetic number, because the mean of its divisors is an integer number (2021760).

Almost surely, 2^21154778 is an apocalyptic number.

21154778 is the 2459-th centered heptagonal number.

21154778 is a deficient number, since it is larger than the sum of its proper divisors (11193382).

21154778 is a wasteful number, since it uses less digits than its factorization.

21154778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 973.

The product of its digits is 15680, while the sum is 35.

The square root of 21154778 is about 4599.4323562805. The cubic root of 21154778 is about 276.5685699222.

The spelling of 21154778 in words is "twenty-one million, one hundred fifty-four thousand, seven hundred seventy-eight".