21507 has 8 divisors (see below), whose sum is σ = 29376. Its totient is φ = 13992.

The previous prime is 21503. The next prime is 21517. The reversal of 21507 is 70512.

It is a happy number.

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

It is not a de Polignac number, because 21507 - 2² = 21503 is a prime.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21507.

It is not an unprimeable number, because it can be changed into a prime (21503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 148 + ... + 254.

It is an arithmetic number, because the mean of its divisors is an integer number (3672).

2²¹⁵⁰⁷ is an apocalyptic number.

21507 is a deficient number, since it is larger than the sum of its proper divisors (7869).

21507 is a wasteful number, since it uses less digits than its factorization.

21507 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 177.

The product of its (nonzero) digits is 70, while the sum is 15.

The square root of 21507 is about 146.6526508455. The cubic root of 21507 is about 27.8095062636.

It can be divided in two parts, 21 and 507, that added together give a triangular number (528 = T₃₂).

The spelling of 21507 in words is "twenty-one thousand, five hundred seven".