21261031 has 24 divisors (see below), whose sum is σ = 24801840. Its totient is φ = 18184320.

The previous prime is 21261029. The next prime is 21261041. The reversal of 21261031 is 13016212.

It is not a de Polignac number, because 21261031 - 2¹ = 21261029 is a prime.

It is a super-2 number, since 2×21261031² = 904062878365922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21260996 and 21261014.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21261041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 256116 + ... + 256198.

It is an arithmetic number, because the mean of its divisors is an integer number (1033410).

Almost surely, 2^21261031 is an apocalyptic number.

21261031 is a deficient number, since it is larger than the sum of its proper divisors (3540809).

21261031 is a wasteful number, since it uses less digits than its factorization.

21261031 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 207 (or 196 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21261031 is about 4610.9685533519. The cubic root of 21261031 is about 277.0308323667.

Adding to 21261031 its reverse (13016212), we get a palindrome (34277243).

The spelling of 21261031 in words is "twenty-one million, two hundred sixty-one thousand, thirty-one".