21505979 has 8 divisors (see below), whose sum is σ = 23502960. Its totient is φ = 19516000.

The previous prime is 21505949. The next prime is 21505999. The reversal of 21505979 is 97950512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21505979 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21505949) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6317 + ... + 9105.

It is an arithmetic number, because the mean of its divisors is an integer number (2937870).

Almost surely, 2^21505979 is an apocalyptic number.

21505979 is a deficient number, since it is larger than the sum of its proper divisors (1996981).

21505979 is a wasteful number, since it uses less digits than its factorization.

21505979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3501.

The product of its (nonzero) digits is 28350, while the sum is 38.

The square root of 21505979 is about 4637.4539350812. The cubic root of 21505979 is about 278.0906619055.

The spelling of 21505979 in words is "twenty-one million, five hundred five thousand, nine hundred seventy-nine".