21501512321557 has 2 divisors, whose sum is σ = 21501512321558. Its totient is φ = 21501512321556.

The previous prime is 21501512321507. The next prime is 21501512321591. The reversal of 21501512321557 is 75512321510512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17020030785156 + 4481481536401 = 4125534^2 + 2116951^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21501512321557 is a prime.

It is a super-2 number, since 2×21501512321557² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21501512321507) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10750756160778 + 10750756160779.

It is an arithmetic number, because the mean of its divisors is an integer number (10750756160779).

Almost surely, 2^{21501512321557} is an apocalyptic number.

It is an amenable number.

21501512321557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21501512321557 is an equidigital number, since it uses as much as digits as its factorization.

21501512321557 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 105000, while the sum is 40.

The spelling of 21501512321557 in words is "twenty-one trillion, five hundred one billion, five hundred twelve million, three hundred twenty-one thousand, five hundred fifty-seven".