21987665501 has 2 divisors, whose sum is σ = 21987665502. Its totient is φ = 21987665500.

The previous prime is 21987665471. The next prime is 21987665521. The reversal of 21987665501 is 10556678912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18961565401 + 3026100100 = 137701^2 + 55010^2 .

It is a cyclic number.

It is not a de Polignac number, because 21987665501 - 2³⁰ = 20913923677 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21987665501.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21987665521) 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, 10993832750 + 10993832751.

It is an arithmetic number, because the mean of its divisors is an integer number (10993832751).

Almost surely, 2^21987665501 is an apocalyptic number.

It is an amenable number.

21987665501 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987665501 is an equidigital number, since it uses as much as digits as its factorization.

21987665501 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 907200, while the sum is 50.

The spelling of 21987665501 in words is "twenty-one billion, nine hundred eighty-seven million, six hundred sixty-five thousand, five hundred one".