20911978 has 4 divisors (see below), whose sum is σ = 31367970. Its totient is φ = 10455988.

The previous prime is 20911963. The next prime is 20912029. The reversal of 20911978 is 87911902.

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., 14845609 + 6066369 = 3853^2 + 2463^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5227993 + ... + 5227996.

Almost surely, 2^20911978 is an apocalyptic number.

20911978 is a deficient number, since it is larger than the sum of its proper divisors (10455992).

20911978 is a wasteful number, since it uses less digits than its factorization.

20911978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10455991.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 20911978 is about 4572.9616224062. The cubic root of 20911978 is about 275.5064079326.

The spelling of 20911978 in words is "twenty million, nine hundred eleven thousand, nine hundred seventy-eight".