21661150549 has 2 divisors, whose sum is σ = 21661150550. Its totient is φ = 21661150548.

The previous prime is 21661150547. The next prime is 21661150561. The reversal of 21661150549 is 94505116612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20446140100 + 1215010449 = 142990^2 + 34857^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661150549 - 2¹ = 21661150547 is a prime.

Together with 21661150547, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661150547) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830575274 + 10830575275.

It is an arithmetic number, because the mean of its divisors is an integer number (10830575275).

Almost surely, 2^21661150549 is an apocalyptic number.

It is an amenable number.

21661150549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661150549 is an equidigital number, since it uses as much as digits as its factorization.

21661150549 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 64800, while the sum is 40.

The spelling of 21661150549 in words is "twenty-one billion, six hundred sixty-one million, one hundred fifty thousand, five hundred forty-nine".