21780387449 has 2 divisors, whose sum is σ = 21780387450. Its totient is φ = 21780387448.

The previous prime is 21780387379. The next prime is 21780387457. The reversal of 21780387449 is 94478308712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11613295225 + 10167092224 = 107765^2 + 100832^2 .

It is a cyclic number.

It is not a de Polignac number, because 21780387449 - 2¹² = 21780383353 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21780387449.

It is not a weakly prime, because it can be changed into another prime (21780387949) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10890193724 + 10890193725.

It is an arithmetic number, because the mean of its divisors is an integer number (10890193725).

Almost surely, 2^21780387449 is an apocalyptic number.

It is an amenable number.

21780387449 is a deficient number, since it is larger than the sum of its proper divisors (1).

21780387449 is an equidigital number, since it uses as much as digits as its factorization.

21780387449 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2709504, while the sum is 53.

The spelling of 21780387449 in words is "twenty-one billion, seven hundred eighty million, three hundred eighty-seven thousand, four hundred forty-nine".