21221378 has 4 divisors (see below), whose sum is σ = 31832070. Its totient is φ = 10610688.

The previous prime is 21221377. The next prime is 21221381. The reversal of 21221378 is 87312212.

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., 18809569 + 2411809 = 4337^2 + 1553^2 .

It is not an unprimeable number, because it can be changed into a prime (21221371) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5305343 + ... + 5305346.

Almost surely, 2^21221378 is an apocalyptic number.

21221378 is a deficient number, since it is larger than the sum of its proper divisors (10610692).

21221378 is a wasteful number, since it uses less digits than its factorization.

21221378 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10610691.

The product of its digits is 1344, while the sum is 26.

The square root of 21221378 is about 4606.6666907863. Note that the first 4 decimals coincide. The cubic root of 21221378 is about 276.8584992383.

The spelling of 21221378 in words is "twenty-one million, two hundred twenty-one thousand, three hundred seventy-eight".