21730505 has 8 divisors (see below), whose sum is σ = 27610632. Its totient is φ = 16361728.

The previous prime is 21730493. The next prime is 21730517. The reversal of 21730505 is 50503712.

It is an interprime number because it is at equal distance from previous prime (21730493) and next prime (21730517).

It can be written as a sum of positive squares in 4 ways, for example, as 173056 + 21557449 = 416^2 + 4643^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21730505 - 2⁶ = 21730441 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 127742 + ... + 127911.

It is an arithmetic number, because the mean of its divisors is an integer number (3451329).

Almost surely, 2^21730505 is an apocalyptic number.

It is an amenable number.

21730505 is a deficient number, since it is larger than the sum of its proper divisors (5880127).

21730505 is a wasteful number, since it uses less digits than its factorization.

21730505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 255675.

The product of its (nonzero) digits is 1050, while the sum is 23.

The square root of 21730505 is about 4661.5989746009. The cubic root of 21730505 is about 279.0550843392.

Adding to 21730505 its sum of digits (23), we get a triangular number (21730528 = T₆₅₉₂).

The spelling of 21730505 in words is "twenty-one million, seven hundred thirty thousand, five hundred five".