81121553 has 2 divisors, whose sum is σ = 81121554. Its totient is φ = 81121552.

The previous prime is 81121543. The next prime is 81121559. The reversal of 81121553 is 35512118.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 79423744 + 1697809 = 8912^2 + 1303^2 .

It is a cyclic number.

It is not a de Polignac number, because 81121553 - 2⁶ = 81121489 is a prime.

It is a super-2 number, since 2×81121553² = 13161412722263618, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81121559) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40560776 + 40560777.

It is an arithmetic number, because the mean of its divisors is an integer number (40560777).

Almost surely, 2^81121553 is an apocalyptic number.

It is an amenable number.

81121553 is a deficient number, since it is larger than the sum of its proper divisors (1).

81121553 is an equidigital number, since it uses as much as digits as its factorization.

81121553 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1200, while the sum is 26.

The square root of 81121553 is about 9006.7504128848. The cubic root of 81121553 is about 432.8911947242.

The spelling of 81121553 in words is "eighty-one million, one hundred twenty-one thousand, five hundred fifty-three".