21264021557 has 2 divisors, whose sum is σ = 21264021558. Its totient is φ = 21264021556.

The previous prime is 21264021553. The next prime is 21264021629. The reversal of 21264021557 is 75512046212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17301193156 + 3962828401 = 131534^2 + 62951^2 .

It is a cyclic number.

It is not a de Polignac number, because 21264021557 - 2² = 21264021553 is a prime.

It is a super-2 number, since 2×21264021557² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21264021553) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10632010778 + 10632010779.

It is an arithmetic number, because the mean of its divisors is an integer number (10632010779).

Almost surely, 2^21264021557 is an apocalyptic number.

It is an amenable number.

21264021557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21264021557 is an equidigital number, since it uses as much as digits as its factorization.

21264021557 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 33600, while the sum is 35.

Adding to 21264021557 its reverse (75512046212), we get a palindrome (96776067769).

The spelling of 21264021557 in words is "twenty-one billion, two hundred sixty-four million, twenty-one thousand, five hundred fifty-seven".