21507131 has 4 divisors (see below), whose sum is σ = 21728952. Its totient is φ = 21285312.

The previous prime is 21507103. The next prime is 21507133. The reversal of 21507131 is 13170512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21507131 is a prime.

It is a super-2 number, since 2×21507131² = 925113367702322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21507133) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 110765 + ... + 110958.

It is an arithmetic number, because the mean of its divisors is an integer number (5432238).

Almost surely, 2^21507131 is an apocalyptic number.

21507131 is a deficient number, since it is larger than the sum of its proper divisors (221821).

21507131 is an equidigital number, since it uses as much as digits as its factorization.

21507131 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 221820.

The product of its (nonzero) digits is 210, while the sum is 20.

The square root of 21507131 is about 4637.5781395034. The cubic root of 21507131 is about 278.0956272646.

Adding to 21507131 its reverse (13170512), we get a palindrome (34677643).

The spelling of 21507131 in words is "twenty-one million, five hundred seven thousand, one hundred thirty-one".