21009023921 has 2 divisors, whose sum is σ = 21009023922. Its totient is φ = 21009023920.

The previous prime is 21009023899. The next prime is 21009023927. The reversal of 21009023921 is 12932090012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20246159521 + 762864400 = 142289^2 + 27620^2 .

It is a cyclic number.

It is not a de Polignac number, because 21009023921 - 2¹⁸ = 21008761777 is a prime.

It is a super-2 number, since 2×21009023921² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21009023927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504511960 + 10504511961.

It is an arithmetic number, because the mean of its divisors is an integer number (10504511961).

Almost surely, 2^21009023921 is an apocalyptic number.

It is an amenable number.

21009023921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009023921 is an equidigital number, since it uses as much as digits as its factorization.

21009023921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1944, while the sum is 29.

The spelling of 21009023921 in words is "twenty-one billion, nine million, twenty-three thousand, nine hundred twenty-one".