21012043021 has 2 divisors, whose sum is σ = 21012043022. Its totient is φ = 21012043020.

The previous prime is 21012042991. The next prime is 21012043043. The reversal of 21012043021 is 12034021012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13785342921 + 7226700100 = 117411^2 + 85010^2 .

It is a cyclic number.

It is not a de Polignac number, because 21012043021 - 2⁷ = 21012042893 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21012042986 and 21012043004.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21012043051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506021510 + 10506021511.

It is an arithmetic number, because the mean of its divisors is an integer number (10506021511).

Almost surely, 2^21012043021 is an apocalyptic number.

It is an amenable number.

21012043021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012043021 is an equidigital number, since it uses as much as digits as its factorization.

21012043021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 16.

Adding to 21012043021 its reverse (12034021012), we get a palindrome (33046064033).

The spelling of 21012043021 in words is "twenty-one billion, twelve million, forty-three thousand, twenty-one".