21240631 has 2 divisors, whose sum is σ = 21240632. Its totient is φ = 21240630.

The previous prime is 21240587. The next prime is 21240643. The reversal of 21240631 is 13604212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21240631 - 2¹⁹ = 20716343 is a prime.

It is a super-2 number, since 2×21240631² = 902328810556322, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21240599 and 21240608.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21241631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10620315 + 10620316.

It is an arithmetic number, because the mean of its divisors is an integer number (10620316).

Almost surely, 2^21240631 is an apocalyptic number.

21240631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21240631 is an equidigital number, since it uses as much as digits as its factorization.

21240631 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21240631 is about 4608.7559058818. The cubic root of 21240631 is about 276.9422001415.

Adding to 21240631 its reverse (13604212), we get a palindrome (34844843).

The spelling of 21240631 in words is "twenty-one million, two hundred forty thousand, six hundred thirty-one".