21316531 has 2 divisors, whose sum is σ = 21316532. Its totient is φ = 21316530.

The previous prime is 21316513. The next prime is 21316553. The reversal of 21316531 is 13561312.

It is a happy number.

Together with previous prime (21316513) it forms an Ormiston pair, because they use the same digits, order apart.

It is an a-pointer prime, because the next prime (21316553) can be obtained adding 21316531 to its sum of digits (22).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21316531 - 2¹⁷ = 21185459 is a prime.

It is a super-2 number, since 2×21316531² = 908788987747922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21316501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10658265 + 10658266.

It is an arithmetic number, because the mean of its divisors is an integer number (10658266).

Almost surely, 2^21316531 is an apocalyptic number.

21316531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21316531 is an equidigital number, since it uses as much as digits as its factorization.

21316531 is an evil number, because the sum of its binary digits is even.

The product of its digits is 540, while the sum is 22.

The square root of 21316531 is about 4616.9828892904. The cubic root of 21316531 is about 277.2716775705.

Adding to 21316531 its reverse (13561312), we get a palindrome (34877843).

The spelling of 21316531 in words is "twenty-one million, three hundred sixteen thousand, five hundred thirty-one".