21151121661 has 24 divisors (see below), whose sum is σ = 31018852800. Its totient is φ = 13885255296.

The previous prime is 21151121623. The next prime is 21151121671. The reversal of 21151121661 is 16612115112.

It is not a de Polignac number, because 21151121661 - 2¹³ = 21151113469 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21151121611) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2437216 + ... + 2445878.

It is an arithmetic number, because the mean of its divisors is an integer number (1292452200).

Almost surely, 2^21151121661 is an apocalyptic number.

It is an amenable number.

21151121661 is a deficient number, since it is larger than the sum of its proper divisors (9867731139).

21151121661 is a wasteful number, since it uses less digits than its factorization.

21151121661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12785 (or 12782 counting only the distinct ones).

The product of its digits is 720, while the sum is 27.

Adding to 21151121661 its reverse (16612115112), we get a palindrome (37763236773).

The spelling of 21151121661 in words is "twenty-one billion, one hundred fifty-one million, one hundred twenty-one thousand, six hundred sixty-one".