21490531 has 2 divisors, whose sum is σ = 21490532. Its totient is φ = 21490530.

The previous prime is 21490529. The next prime is 21490541. The reversal of 21490531 is 13509412.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21490531 - 2¹ = 21490529 is a prime.

It is a super-2 number, since 2×21490531² = 923685845323922, which contains 22 as substring.

Together with 21490529, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21490496 and 21490505.

It is not a weakly prime, because it can be changed into another prime (21490541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10745265 + 10745266.

It is an arithmetic number, because the mean of its divisors is an integer number (10745266).

Almost surely, 2^21490531 is an apocalyptic number.

21490531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21490531 is an equidigital number, since it uses as much as digits as its factorization.

21490531 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 21490531 is about 4635.7880667692. The cubic root of 21490531 is about 278.0240606817.

Adding to 21490531 its reverse (13509412), we get a palindrome (34999943).

The spelling of 21490531 in words is "twenty-one million, four hundred ninety thousand, five hundred thirty-one".