21690329 has 2 divisors, whose sum is σ = 21690330. Its totient is φ = 21690328.

The previous prime is 21690293. The next prime is 21690337. The reversal of 21690329 is 92309612.

Together with previous prime (21690293) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13579225 + 8111104 = 3685^2 + 2848^2 .

It is a cyclic number.

It is not a de Polignac number, because 21690329 - 2²⁴ = 4913113 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21690295 and 21690304.

It is not a weakly prime, because it can be changed into another prime (21690349) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845164 + 10845165.

It is an arithmetic number, because the mean of its divisors is an integer number (10845165).

Almost surely, 2^21690329 is an apocalyptic number.

It is an amenable number.

21690329 is a deficient number, since it is larger than the sum of its proper divisors (1).

21690329 is an equidigital number, since it uses as much as digits as its factorization.

21690329 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5832, while the sum is 32.

The square root of 21690329 is about 4657.2877299991. The cubic root of 21690329 is about 278.8830031497.

The spelling of 21690329 in words is "twenty-one million, six hundred ninety thousand, three hundred twenty-nine".