21723505 has 16 divisors (see below), whose sum is σ = 26712000. Its totient is φ = 16954560.

The previous prime is 21723469. The next prime is 21723539. The reversal of 21723505 is 50532712.

It is not a de Polignac number, because 21723505 - 2¹¹ = 21721457 is a prime.

It is a super-3 number, since 3×21723505³ (a number of 23 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21723505.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 62071 + ... + 62419.

It is an arithmetic number, because the mean of its divisors is an integer number (1669500).

Almost surely, 2^21723505 is an apocalyptic number.

It is an amenable number.

21723505 is a deficient number, since it is larger than the sum of its proper divisors (4988495).

21723505 is a wasteful number, since it uses less digits than its factorization.

21723505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 624.

The product of its (nonzero) digits is 2100, while the sum is 25.

The square root of 21723505 is about 4660.8480987906. The cubic root of 21723505 is about 279.0251173201.

The spelling of 21723505 in words is "twenty-one million, seven hundred twenty-three thousand, five hundred five".