30721021 has 2 divisors, whose sum is σ = 30721022. Its totient is φ = 30721020.

The previous prime is 30721001. The next prime is 30721027. The reversal of 30721021 is 12012703.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 28196100 + 2524921 = 5310^2 + 1589^2 .

It is a cyclic number.

It is not a de Polignac number, because 30721021 - 2⁹ = 30720509 is a prime.

It is a super-2 number, since 2×30721021² = 1887562262564882, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 30720986 and 30721004.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (30721027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15360510 + 15360511.

It is an arithmetic number, because the mean of its divisors is an integer number (15360511).

Almost surely, 2^30721021 is an apocalyptic number.

It is an amenable number.

30721021 is a deficient number, since it is larger than the sum of its proper divisors (1).

30721021 is an equidigital number, since it uses as much as digits as its factorization.

30721021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 84, while the sum is 16.

The square root of 30721021 is about 5542.6546888653. The cubic root of 30721021 is about 313.1928809425.

Adding to 30721021 its reverse (12012703), we get a palindrome (42733724).

The spelling of 30721021 in words is "thirty million, seven hundred twenty-one thousand, twenty-one".