21251378 has 4 divisors (see below), whose sum is σ = 31877070. Its totient is φ = 10625688.

The previous prime is 21251353. The next prime is 21251381. The reversal of 21251378 is 87315212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 16265089 + 4986289 = 4033^2 + 2233^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21251378.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5312843 + ... + 5312846.

Almost surely, 2^21251378 is an apocalyptic number.

21251378 is a deficient number, since it is larger than the sum of its proper divisors (10625692).

21251378 is a wasteful number, since it uses less digits than its factorization.

21251378 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10625691.

The product of its digits is 3360, while the sum is 29.

The square root of 21251378 is about 4609.9216913089. The cubic root of 21251378 is about 276.9888998841.

The spelling of 21251378 in words is "twenty-one million, two hundred fifty-one thousand, three hundred seventy-eight".