21729361 has 2 divisors, whose sum is σ = 21729362. Its totient is φ = 21729360.

The previous prime is 21729341. The next prime is 21729377. The reversal of 21729361 is 16392712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13549761 + 8179600 = 3681^2 + 2860^2 .

It is a cyclic number.

It is not a de Polignac number, because 21729361 - 2⁵ = 21729329 is a prime.

It is not a weakly prime, because it can be changed into another prime (21729341) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10864680 + 10864681.

It is an arithmetic number, because the mean of its divisors is an integer number (10864681).

Almost surely, 2^21729361 is an apocalyptic number.

It is an amenable number.

21729361 is a deficient number, since it is larger than the sum of its proper divisors (1).

21729361 is an equidigital number, since it uses as much as digits as its factorization.

21729361 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4536, while the sum is 31.

The square root of 21729361 is about 4661.4762683081. The cubic root of 21729361 is about 279.0501873120.

The spelling of 21729361 in words is "twenty-one million, seven hundred twenty-nine thousand, three hundred sixty-one".