20661516551 has 4 divisors (see below), whose sum is σ = 22250863992. Its totient is φ = 19072169112.

The previous prime is 20661516521. The next prime is 20661516553. The reversal of 20661516551 is 15561516602.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 15561516602 = 2 ⋅7780758301.

It is a cyclic number.

It is not a de Polignac number, because 20661516551 - 2¹⁰ = 20661515527 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20661516553) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 794673701 + ... + 794673726.

It is an arithmetic number, because the mean of its divisors is an integer number (5562715998).

Almost surely, 2^20661516551 is an apocalyptic number.

20661516551 is a deficient number, since it is larger than the sum of its proper divisors (1589347441).

20661516551 is a wasteful number, since it uses less digits than its factorization.

20661516551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1589347440.

The product of its (nonzero) digits is 54000, while the sum is 38.

It can be divided in two parts, 2066151 and 6551, that added together give a palindrome (2072702).

The spelling of 20661516551 in words is "twenty billion, six hundred sixty-one million, five hundred sixteen thousand, five hundred fifty-one".