661556011 has 2 divisors, whose sum is σ = 661556012. Its totient is φ = 661556010.

The previous prime is 661556009. The next prime is 661556047. The reversal of 661556011 is 110655166.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 661556011 - 2¹ = 661556009 is a prime.

Together with 661556009, it forms a pair of twin primes.

It is a Chen prime.

It is equal to p_34362913 and since 661556011 and 34362913 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (661556111) 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, 330778005 + 330778006.

It is an arithmetic number, because the mean of its divisors is an integer number (330778006).

Almost surely, 2^661556011 is an apocalyptic number.

661556011 is a deficient number, since it is larger than the sum of its proper divisors (1).

661556011 is an equidigital number, since it uses as much as digits as its factorization.

661556011 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5400, while the sum is 31.

The square root of 661556011 is about 25720.7311521271. The cubic root of 661556011 is about 871.3424516230.

It can be divided in two parts, 6615 and 56011, that added together give a palindrome (62626).

The spelling of 661556011 in words is "six hundred sixty-one million, five hundred fifty-six thousand, eleven".