21017931 has 16 divisors (see below), whose sum is σ = 30650880. Its totient is φ = 12705120.

The previous prime is 21017897. The next prime is 21017951. The reversal of 21017931 is 13971012.

It is not a de Polignac number, because 21017931 - 2⁷ = 21017803 is a prime.

It is a super-2 number, since 2×21017931² = 883506847041522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21017951) 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 in 15 ways as a sum of consecutive naturals, for example, 19710 + ... + 20748.

It is an arithmetic number, because the mean of its divisors is an integer number (1915680).

Almost surely, 2^21017931 is an apocalyptic number.

21017931 is a deficient number, since it is larger than the sum of its proper divisors (9632949).

21017931 is a wasteful number, since it uses less digits than its factorization.

21017931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1666.

The product of its (nonzero) digits is 378, while the sum is 24.

The square root of 21017931 is about 4584.5317100005. The cubic root of 21017931 is about 275.9709195364.

Adding to 21017931 its reverse (13971012), we get a palindrome (34988943).

The spelling of 21017931 in words is "twenty-one million, seventeen thousand, nine hundred thirty-one".