21913729 has 2 divisors, whose sum is σ = 21913730. Its totient is φ = 21913728.

The previous prime is 21913711. The next prime is 21913739. The reversal of 21913729 is 92731912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19158129 + 2755600 = 4377^2 + 1660^2 .

It is a cyclic number.

It is not a de Polignac number, because 21913729 - 2⁷ = 21913601 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21913694 and 21913703.

It is not a weakly prime, because it can be changed into another prime (21913709) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10956864 + 10956865.

It is an arithmetic number, because the mean of its divisors is an integer number (10956865).

Almost surely, 2^21913729 is an apocalyptic number.

It is an amenable number.

21913729 is a deficient number, since it is larger than the sum of its proper divisors (1).

21913729 is an equidigital number, since it uses as much as digits as its factorization.

21913729 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6804, while the sum is 34.

The square root of 21913729 is about 4681.2102067735. The cubic root of 21913729 is about 279.8371885117.

The spelling of 21913729 in words is "twenty-one million, nine hundred thirteen thousand, seven hundred twenty-nine".