21011918 has 4 divisors (see below), whose sum is σ = 31517880. Its totient is φ = 10505958.

The previous prime is 21011917. The next prime is 21011923. The reversal of 21011918 is 81911012.

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

It is a junction number, because it is equal to n+sod(n) for n = 21011893 and 21011902.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011917) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5252978 + ... + 5252981.

It is an arithmetic number, because the mean of its divisors is an integer number (7879470).

Almost surely, 2^21011918 is an apocalyptic number.

21011918 is a deficient number, since it is larger than the sum of its proper divisors (10505962).

21011918 is a wasteful number, since it uses less digits than its factorization.

21011918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10505961.

The product of its (nonzero) digits is 144, while the sum is 23.

The square root of 21011918 is about 4583.8758709197. The cubic root of 21011918 is about 275.9445996065.

The spelling of 21011918 in words is "twenty-one million, eleven thousand, nine hundred eighteen".