21261630 has 32 divisors (see below), whose sum is σ = 54954144. Its totient is φ = 5233536.

The previous prime is 21261623. The next prime is 21261631. The reversal of 21261630 is 3616212.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21261597 and 21261606.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21261631) 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 15 ways as a sum of consecutive naturals, for example, 26869 + ... + 27648.

It is an arithmetic number, because the mean of its divisors is an integer number (1717317).

Almost surely, 2^21261630 is an apocalyptic number.

21261630 is an abundant number, since it is smaller than the sum of its proper divisors (33692514).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21261630 is a wasteful number, since it uses less digits than its factorization.

21261630 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54540.

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 21261630 is about 4611.0335067097. The cubic root of 21261630 is about 277.0334339952.

Adding to 21261630 its reverse (3616212), we get a palindrome (24877842).

The spelling of 21261630 in words is "twenty-one million, two hundred sixty-one thousand, six hundred thirty".