21541978 has 4 divisors (see below), whose sum is σ = 32312970. Its totient is φ = 10770988.

The previous prime is 21541969. The next prime is 21541979. The reversal of 21541978 is 87914512.

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 + 2732409 = 4337^2 + 1653^2 .

It is not an unprimeable number, because it can be changed into a prime (21541979) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5385493 + ... + 5385496.

Almost surely, 2^21541978 is an apocalyptic number.

21541978 is a deficient number, since it is larger than the sum of its proper divisors (10770992).

21541978 is a wasteful number, since it uses less digits than its factorization.

21541978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10770991.

The product of its digits is 20160, while the sum is 37.

The square root of 21541978 is about 4641.3336445466. Note that the first 3 decimals coincide. The cubic root of 21541978 is about 278.2457413389.

The spelling of 21541978 in words is "twenty-one million, five hundred forty-one thousand, nine hundred seventy-eight".