21751987 has 8 divisors (see below), whose sum is σ = 22512512. Its totient is φ = 20995200.

The previous prime is 21751981. The next prime is 21751991. The reversal of 21751987 is 78915712.

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 21751987 - 2¹⁵ = 21719219 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21751981) 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, 16123 + ... + 17419.

It is an arithmetic number, because the mean of its divisors is an integer number (2814064).

Almost surely, 2^21751987 is an apocalyptic number.

21751987 is a deficient number, since it is larger than the sum of its proper divisors (760525).

21751987 is a wasteful number, since it uses less digits than its factorization.

21751987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1869.

The product of its digits is 35280, while the sum is 40.

The square root of 21751987 is about 4663.9025504399. The cubic root of 21751987 is about 279.1470086799.

The spelling of 21751987 in words is "twenty-one million, seven hundred fifty-one thousand, nine hundred eighty-seven".