21261320 has 32 divisors (see below), whose sum is σ = 47983320. Its totient is φ = 8478720.

The previous prime is 21261293. The next prime is 21261337. The reversal of 21261320 is 2316212.

It is a Cunningham number, because it is equal to 4611²-1.

It can be written as a sum of positive squares in 4 ways, for example, as 18028516 + 3232804 = 4246^2 + 1798^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 17864 + ... + 19016.

Almost surely, 2^21261320 is an apocalyptic number.

21261320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21261320 is an abundant number, since it is smaller than the sum of its proper divisors (26722000).

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

21261320 is a wasteful number, since it uses less digits than its factorization.

21261320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1625 (or 1621 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 17.

The square root of 21261320 is about 4610.9998915637. Note that the first 3 decimals coincide. The cubic root of 21261320 is about 277.0320875825.

Adding to 21261320 its reverse (2316212), we get a palindrome (23577532).

The spelling of 21261320 in words is "twenty-one million, two hundred sixty-one thousand, three hundred twenty".