21756039421 has 2 divisors, whose sum is σ = 21756039422. Its totient is φ = 21756039420.

The previous prime is 21756039373. The next prime is 21756039427. The reversal of 21756039421 is 12493065712.

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., 19491231321 + 2264808100 = 139611^2 + 47590^2 .

It is a cyclic number.

It is not a de Polignac number, because 21756039421 - 2⁷ = 21756039293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21756039427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10878019710 + 10878019711.

It is an arithmetic number, because the mean of its divisors is an integer number (10878019711).

Almost surely, 2^21756039421 is an apocalyptic number.

It is an amenable number.

21756039421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21756039421 is an equidigital number, since it uses as much as digits as its factorization.

21756039421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 90720, while the sum is 40.

The spelling of 21756039421 in words is "twenty-one billion, seven hundred fifty-six million, thirty-nine thousand, four hundred twenty-one".