21436516861 has 2 divisors, whose sum is σ = 21436516862. Its totient is φ = 21436516860.

The previous prime is 21436516807. The next prime is 21436516939. The reversal of 21436516861 is 16861563412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21114996100 + 321520761 = 145310^2 + 17931^2 .

It is a cyclic number.

It is not a de Polignac number, because 21436516861 - 2¹⁹ = 21435992573 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21436586861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10718258430 + 10718258431.

It is an arithmetic number, because the mean of its divisors is an integer number (10718258431).

Almost surely, 2^21436516861 is an apocalyptic number.

It is an amenable number.

21436516861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21436516861 is an equidigital number, since it uses as much as digits as its factorization.

21436516861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 207360, while the sum is 43.

It can be divided in two parts, 2143651 and 6861, that added together give a palindrome (2150512).

The spelling of 21436516861 in words is "twenty-one billion, four hundred thirty-six million, five hundred sixteen thousand, eight hundred sixty-one".