21210721505437 has 2 divisors, whose sum is σ = 21210721505438. Its totient is φ = 21210721505436.

The previous prime is 21210721505399. The next prime is 21210721505461. The reversal of 21210721505437 is 73450512701212.

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., 16688948914521 + 4521772590916 = 4085211^2 + 2126446^2 .

It is a cyclic number.

It is not a de Polignac number, because 21210721505437 - 2²⁷ = 21210587287709 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21210721505437.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21210721505497) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605360752718 + 10605360752719.

It is an arithmetic number, because the mean of its divisors is an integer number (10605360752719).

Almost surely, 2^{21210721505437} is an apocalyptic number.

It is an amenable number.

21210721505437 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210721505437 is an equidigital number, since it uses as much as digits as its factorization.

21210721505437 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 117600, while the sum is 40.

The spelling of 21210721505437 in words is "twenty-one trillion, two hundred ten billion, seven hundred twenty-one million, five hundred five thousand, four hundred thirty-seven".