21878304781 has 2 divisors, whose sum is σ = 21878304782. Its totient is φ = 21878304780.

The previous prime is 21878304757. The next prime is 21878304797. The reversal of 21878304781 is 18740387812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16499402500 + 5378902281 = 128450^2 + 73341^2 .

It is a cyclic number.

It is not a de Polignac number, because 21878304781 - 2¹⁹ = 21877780493 is a prime.

It is a super-2 number, since 2×21878304781² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21878305781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10939152390 + 10939152391.

It is an arithmetic number, because the mean of its divisors is an integer number (10939152391).

Almost surely, 2^21878304781 is an apocalyptic number.

It is an amenable number.

21878304781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21878304781 is an equidigital number, since it uses as much as digits as its factorization.

21878304781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 602112, while the sum is 49.

The spelling of 21878304781 in words is "twenty-one billion, eight hundred seventy-eight million, three hundred four thousand, seven hundred eighty-one".