21587431 has 2 divisors, whose sum is σ = 21587432. Its totient is φ = 21587430.

The previous prime is 21587417. The next prime is 21587453. The reversal of 21587431 is 13478512.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21587431 is a prime.

It is a super-2 number, since 2×21587431² = 932034354359522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21587393 and 21587402.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21587411) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10793715 + 10793716.

It is an arithmetic number, because the mean of its divisors is an integer number (10793716).

Almost surely, 2^21587431 is an apocalyptic number.

21587431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21587431 is an equidigital number, since it uses as much as digits as its factorization.

21587431 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6720, while the sum is 31.

The square root of 21587431 is about 4646.2276095775. The cubic root of 21587431 is about 278.4413008967.

The spelling of 21587431 in words is "twenty-one million, five hundred eighty-seven thousand, four hundred thirty-one".