21267555557 has 4 divisors (see below), whose sum is σ = 21478125516. Its totient is φ = 21056985600.

The previous prime is 21267555527. The next prime is 21267555587. The reversal of 21267555557 is 75555576212.

It is a Cunningham number, because it is equal to 145834²+1.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21267555527) and next prime (21267555587).

It can be written as a sum of positive squares in 2 ways, for example, as 20433558916 + 833996641 = 142946^2 + 28879^2 .

It is a cyclic number.

It is not a de Polignac number, because 21267555557 - 2¹⁰ = 21267554533 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 (21267555527) 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, 105284828 + ... + 105285029.

It is an arithmetic number, because the mean of its divisors is an integer number (5369531379).

Almost surely, 2^21267555557 is an apocalyptic number.

It is an amenable number.

21267555557 is a deficient number, since it is larger than the sum of its proper divisors (210569959).

21267555557 is a wasteful number, since it uses less digits than its factorization.

21267555557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 210569958.

The product of its digits is 3675000, while the sum is 50.

It can be divided in two parts, 2126755 and 5557, that added together give a palindrome (2132312).

The spelling of 21267555557 in words is "twenty-one billion, two hundred sixty-seven million, five hundred fifty-five thousand, five hundred fifty-seven".