661551521 has 2 divisors, whose sum is σ = 661551522. Its totient is φ = 661551520.

The previous prime is 661551503. The next prime is 661551529. The reversal of 661551521 is 125155166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 582981025 + 78570496 = 24145^2 + 8864^2 .

It is a cyclic number.

It is not a de Polignac number, because 661551521 - 2¹⁰ = 661550497 is a prime.

It is not a weakly prime, because it can be changed into another prime (661551529) 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, 330775760 + 330775761.

It is an arithmetic number, because the mean of its divisors is an integer number (330775761).

Almost surely, 2^661551521 is an apocalyptic number.

It is an amenable number.

661551521 is a deficient number, since it is larger than the sum of its proper divisors (1).

661551521 is an equidigital number, since it uses as much as digits as its factorization.

661551521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9000, while the sum is 32.

The square root of 661551521 is about 25720.6438683016. The cubic root of 661551521 is about 871.3404803430.

It can be divided in two parts, 66155 and 1521, that added together give a palindrome (67676).

The spelling of 661551521 in words is "six hundred sixty-one million, five hundred fifty-one thousand, five hundred twenty-one".