21081730 has 16 divisors (see below), whose sum is σ = 38324664. Its totient is φ = 8348800.

The previous prime is 21081727. The next prime is 21081733. The reversal of 21081730 is 3718012.

It is an interprime number because it is at equal distance from previous prime (21081727) and next prime (21081733).

It can be written as a sum of positive squares in 4 ways, for example, as 19686969 + 1394761 = 4437^2 + 1181^2 .

It is not an unprimeable number, because it can be changed into a prime (21081733) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9427 + ... + 11446.

Almost surely, 2^21081730 is an apocalyptic number.

21081730 is a deficient number, since it is larger than the sum of its proper divisors (17242934).

21081730 is a wasteful number, since it uses less digits than its factorization.

21081730 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20981.

The product of its (nonzero) digits is 336, while the sum is 22.

The square root of 21081730 is about 4591.4845093934. The cubic root of 21081730 is about 276.2498699862.

Adding to 21081730 its reverse (3718012), we get a palindrome (24799742).

The spelling of 21081730 in words is "twenty-one million, eighty-one thousand, seven hundred thirty".