1661626261 has 2 divisors, whose sum is σ = 1661626262. Its totient is φ = 1661626260.

The previous prime is 1661626259. The next prime is 1661626321. The reversal of 1661626261 is 1626261661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 992628036 + 668998225 = 31506^2 + 25865^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661626261 - 2¹ = 1661626259 is a prime.

It is a super-2 number, since 2×1661626261² = 5522003662489680242, which contains 22 as substring.

Together with 1661626259, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 1661626261.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661626201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830813130 + 830813131.

It is an arithmetic number, because the mean of its divisors is an integer number (830813131).

Almost surely, 2^1661626261 is an apocalyptic number.

It is an amenable number.

1661626261 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661626261 is an equidigital number, since it uses as much as digits as its factorization.

1661626261 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 37.

The square root of 1661626261 is about 40763.0501925457. The cubic root of 1661626261 is about 1184.4346822527.

The spelling of 1661626261 in words is "one billion, six hundred sixty-one million, six hundred twenty-six thousand, two hundred sixty-one".