21428978 has 8 divisors (see below), whose sum is σ = 32927580. Its totient is φ = 10453120.

The previous prime is 21428971. The next prime is 21428989. The reversal of 21428978 is 87982412.

It can be written as a sum of positive squares in 2 ways, for example, as 19035769 + 2393209 = 4363^2 + 1547^2 .

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

It is a Harshad number since it is a multiple of its sum of digits (41).

It is not an unprimeable number, because it can be changed into a prime (21428971) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 130583 + ... + 130746.

Almost surely, 2^21428978 is an apocalyptic number.

21428978 is a deficient number, since it is larger than the sum of its proper divisors (11498602).

21428978 is a wasteful number, since it uses less digits than its factorization.

21428978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 261372.

The product of its digits is 64512, while the sum is 41.

The square root of 21428978 is about 4629.1444133879. The cubic root of 21428978 is about 277.7583687891.

It can be divided in two parts, 214 and 28978, that added together give a palindrome (29192).

The spelling of 21428978 in words is "twenty-one million, four hundred twenty-eight thousand, nine hundred seventy-eight".