55781957521 has 2 divisors, whose sum is σ = 55781957522. Its totient is φ = 55781957520.

The previous prime is 55781957449. The next prime is 55781957551. The reversal of 55781957521 is 12575918755.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 38269140625 + 17512816896 = 195625^2 + 132336^2 .

It is a cyclic number.

It is not a de Polignac number, because 55781957521 - 2⁹ = 55781957009 is a prime.

It is a super-2 number, since 2×55781957521² (a number of 22 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (55781957551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 27890978760 + 27890978761.

It is an arithmetic number, because the mean of its divisors is an integer number (27890978761).

Almost surely, 2^55781957521 is an apocalyptic number.

It is an amenable number.

55781957521 is a deficient number, since it is larger than the sum of its proper divisors (1).

55781957521 is an equidigital number, since it uses as much as digits as its factorization.

55781957521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4410000, while the sum is 55.

The spelling of 55781957521 in words is "fifty-five billion, seven hundred eighty-one million, nine hundred fifty-seven thousand, five hundred twenty-one".