21187131 has 8 divisors (see below), whose sum is σ = 32285184. Its totient is φ = 12106920.

The previous prime is 21187129. The next prime is 21187189. The reversal of 21187131 is 13178112.

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 21187131 - 2¹ = 21187129 is a prime.

It is a super-2 number, since 2×21187131² = 897789040022322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21187931) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 504435 + ... + 504476.

It is an arithmetic number, because the mean of its divisors is an integer number (4035648).

Almost surely, 2^21187131 is an apocalyptic number.

21187131 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21187131 is a deficient number, since it is larger than the sum of its proper divisors (11098053).

21187131 is a wasteful number, since it uses less digits than its factorization.

21187131 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1008921.

The product of its digits is 336, while the sum is 24.

The square root of 21187131 is about 4602.9480770480. The cubic root of 21187131 is about 276.7094878963.

Subtracting from 21187131 its product of digits (336), we obtain a triangular number (21186795 = T₆₅₀₉).

The spelling of 21187131 in words is "twenty-one million, one hundred eighty-seven thousand, one hundred thirty-one".