21123730 has 16 divisors (see below), whose sum is σ = 38280600. Its totient is φ = 8392192.

The previous prime is 21123721. The next prime is 21123757. The reversal of 21123730 is 3732112.

It can be written as a sum of positive squares in 4 ways, for example, as 19000881 + 2122849 = 4359^2 + 1457^2 .

It is a super-2 number, since 2×21123730² = 892423938225800, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21123698 and 21123707.

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, 5599 + ... + 8578.

Almost surely, 2^21123730 is an apocalyptic number.

21123730 is a deficient number, since it is larger than the sum of its proper divisors (17156870).

21123730 is a wasteful number, since it uses less digits than its factorization.

21123730 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14333.

The product of its (nonzero) digits is 252, while the sum is 19.

The square root of 21123730 is about 4596.0559178496. The cubic root of 21123730 is about 276.4332008932.

Adding to 21123730 its reverse (3732112), we get a palindrome (24855842).

It can be divided in two parts, 211 and 23730, that multiplied together give a triangular number (5007030 = T₃₁₆₄).

The spelling of 21123730 in words is "twenty-one million, one hundred twenty-three thousand, seven hundred thirty".