21731291 has 2 divisors, whose sum is σ = 21731292. Its totient is φ = 21731290.

The previous prime is 21731273. The next prime is 21731317. The reversal of 21731291 is 19213712.

It is an a-pointer prime, because the next prime (21731317) can be obtained adding 21731291 to its sum of digits (26).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21731291 - 2¹⁴ = 21714907 is a prime.

It is a Chen prime.

It is equal to p_1373291 and since 21731291 and 1373291 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21731291.

It is not a weakly prime, because it can be changed into another prime (21731191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10865645 + 10865646.

It is an arithmetic number, because the mean of its divisors is an integer number (10865646).

Almost surely, 2^21731291 is an apocalyptic number.

21731291 is a deficient number, since it is larger than the sum of its proper divisors (1).

21731291 is an equidigital number, since it uses as much as digits as its factorization.

21731291 is an evil number, because the sum of its binary digits is even.

The product of its digits is 756, while the sum is 26.

The square root of 21731291 is about 4661.6832796748. The cubic root of 21731291 is about 279.0584488054.

It can be divided in two parts, 21731 and 291, that added together give a palindrome (22022).

The spelling of 21731291 in words is "twenty-one million, seven hundred thirty-one thousand, two hundred ninety-one".