21887461721 has 2 divisors, whose sum is σ = 21887461722. Its totient is φ = 21887461720.

The previous prime is 21887461679. The next prime is 21887461723. The reversal of 21887461721 is 12716478812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13441851721 + 8445610000 = 115939^2 + 91900^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21887461721 is a prime.

Together with 21887461723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21887461723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10943730860 + 10943730861.

It is an arithmetic number, because the mean of its divisors is an integer number (10943730861).

Almost surely, 2^21887461721 is an apocalyptic number.

It is an amenable number.

21887461721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21887461721 is an equidigital number, since it uses as much as digits as its factorization.

21887461721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 301056, while the sum is 47.

The spelling of 21887461721 in words is "twenty-one billion, eight hundred eighty-seven million, four hundred sixty-one thousand, seven hundred twenty-one".