21561330 has 32 divisors (see below), whose sum is σ = 59140224. Its totient is φ = 4928256.

The previous prime is 21561329. The next prime is 21561341. The reversal of 21561330 is 3316512.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21561297 and 21561306.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 51127 + ... + 51546.

It is an arithmetic number, because the mean of its divisors is an integer number (1848132).

Almost surely, 2^21561330 is an apocalyptic number.

21561330 is an abundant number, since it is smaller than the sum of its proper divisors (37578894).

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

21561330 is a wasteful number, since it uses less digits than its factorization.

21561330 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 102690.

The product of its (nonzero) digits is 540, while the sum is 21.

The square root of 21561330 is about 4643.4179221776. The cubic root of 21561330 is about 278.3290360730.

Adding to 21561330 its reverse (3316512), we get a palindrome (24877842).

It can be divided in two parts, 2156 and 1330, that added together give a triangular number (3486 = T₈₃).

The spelling of 21561330 in words is "twenty-one million, five hundred sixty-one thousand, three hundred thirty".