21587391 has 60 divisors (see below), whose sum is σ = 38743432. Its totient is φ = 12002256.

The previous prime is 21587389. The next prime is 21587411. The reversal of 21587391 is 19378512.

It is not a de Polignac number, because 21587391 - 2¹ = 21587389 is a prime.

Its product of digits (15120) is a multiple of the sum of its prime factors (80).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21587311) by changing a digit.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 583425 + ... + 583461.

Almost surely, 2^21587391 is an apocalyptic number.

21587391 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21587391 is a deficient number, since it is larger than the sum of its proper divisors (17156041).

21587391 is an frugal number, since it uses more digits than its factorization.

21587391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80 (or 47 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 21587391 is about 4646.2233050081. The cubic root of 21587391 is about 278.4411289191.

The spelling of 21587391 in words is "twenty-one million, five hundred eighty-seven thousand, three hundred ninety-one".