661155241202581 has 2 divisors, whose sum is σ = 661155241202582. Its totient is φ = 661155241202580.

The previous prime is 661155241202569. The next prime is 661155241202641. The reversal of 661155241202581 is 185202142551166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 397954262361681 + 263200978840900 = 19948791^2 + 16223470^2 .

It is a cyclic number.

It is not a de Polignac number, because 661155241202581 - 2¹³ = 661155241194389 is a prime.

It is a super-2 number, since 2×661155241202581² (a number of 30 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661155241242581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330577620601290 + 330577620601291.

It is an arithmetic number, because the mean of its divisors is an integer number (330577620601291).

Almost surely, 2^{661155241202581} is an apocalyptic number.

It is an amenable number.

661155241202581 is a deficient number, since it is larger than the sum of its proper divisors (1).

661155241202581 is an equidigital number, since it uses as much as digits as its factorization.

661155241202581 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1152000, while the sum is 49.

The spelling of 661155241202581 in words is "six hundred sixty-one trillion, one hundred fifty-five billion, two hundred forty-one million, two hundred two thousand, five hundred eighty-one".