21072778 has 8 divisors (see below), whose sum is σ = 31628772. Its totient is φ = 10529856.

The previous prime is 21072769. The next prime is 21072823. The reversal of 21072778 is 87727012.

It can be written as a sum of positive squares in 2 ways, for example, as 15657849 + 5414929 = 3957^2 + 2327^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3976 + ... + 7612.

Almost surely, 2^21072778 is an apocalyptic number.

21072778 is a deficient number, since it is larger than the sum of its proper divisors (10555994).

21072778 is a wasteful number, since it uses less digits than its factorization.

21072778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6536.

The product of its (nonzero) digits is 10976, while the sum is 34.

The square root of 21072778 is about 4590.5095577724. The cubic root of 21072778 is about 276.2107628390.

It can be divided in two parts, 2 and 1072778, that multiplied together give a triangular number (2145556 = T₂₀₇₁).

The spelling of 21072778 in words is "twenty-one million, seventy-two thousand, seven hundred seventy-eight".