21253978 has 16 divisors (see below), whose sum is σ = 35225280. Its totient is φ = 9566656.

The previous prime is 21253963. The next prime is 21253979. The reversal of 21253978 is 87935212.

It is not an unprimeable number, because it can be changed into a prime (21253979) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12808 + ... + 14371.

It is an arithmetic number, because the mean of its divisors is an integer number (2201580).

Almost surely, 2^21253978 is an apocalyptic number.

21253978 is a deficient number, since it is larger than the sum of its proper divisors (13971302).

21253978 is a wasteful number, since it uses less digits than its factorization.

21253978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27221.

The product of its digits is 30240, while the sum is 37.

The square root of 21253978 is about 4610.2036831359. The cubic root of 21253978 is about 277.0001954931. Note that the first 3 decimals are identical.

The spelling of 21253978 in words is "twenty-one million, two hundred fifty-three thousand, nine hundred seventy-eight".