21837187561 has 12 divisors (see below), whose sum is σ = 25410131460. Its totient is φ = 18711924000.

The previous prime is 21837187523. The next prime is 21837187607. The reversal of 21837187561 is 16578173812.

It can be written as a sum of positive squares in 2 ways, for example, as 20033571600 + 1803615961 = 141540^2 + 42469^2 .

It is not a de Polignac number, because 21837187561 - 2¹⁵ = 21837154793 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (49).

It is not an unprimeable number, because it can be changed into a prime (21837187501) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 100311 + ... + 231811.

It is an arithmetic number, because the mean of its divisors is an integer number (2117510955).

Almost surely, 2^21837187561 is an apocalyptic number.

It is an amenable number.

21837187561 is a deficient number, since it is larger than the sum of its proper divisors (3572943899).

21837187561 is a wasteful number, since it uses less digits than its factorization.

21837187561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 134904 (or 134897 counting only the distinct ones).

The product of its digits is 564480, while the sum is 49.

The spelling of 21837187561 in words is "twenty-one billion, eight hundred thirty-seven million, one hundred eighty-seven thousand, five hundred sixty-one".