21729031 has 2 divisors, whose sum is σ = 21729032. Its totient is φ = 21729030.

The previous prime is 21729017. The next prime is 21729079. The reversal of 21729031 is 13092712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21729031 - 2²³ = 13340423 is a prime.

It is a super-2 number, since 2×21729031² = 944301576397922, which contains 22 as substring.

It is equal to p_1373164 and since 21729031 and 1373164 have the same sum of digits, it is a Honaker prime.

It is a junction number, because it is equal to n+sod(n) for n = 21728987 and 21729005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21729131) 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 as a sum of consecutive naturals, namely, 10864515 + 10864516.

It is an arithmetic number, because the mean of its divisors is an integer number (10864516).

Almost surely, 2^21729031 is an apocalyptic number.

21729031 is a deficient number, since it is larger than the sum of its proper divisors (1).

21729031 is an equidigital number, since it uses as much as digits as its factorization.

21729031 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 21729031 is about 4661.4408716619. The cubic root of 21729031 is about 279.0487746761.

The spelling of 21729031 in words is "twenty-one million, seven hundred twenty-nine thousand, thirty-one".