1551661 has 2 divisors, whose sum is σ = 1551662. Its totient is φ = 1551660.

The previous prime is 1551659. The next prime is 1551677. The reversal of 1551661 is 1661551.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1425636 + 126025 = 1194^2 + 355^2 .

It is a cyclic number.

It is not a de Polignac number, because 1551661 - 2¹ = 1551659 is a prime.

Together with 1551659, it forms a pair of twin primes.

It is an Ulam number.

1551661 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1551601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 775830 + 775831.

It is an arithmetic number, because the mean of its divisors is an integer number (775831).

2^1551661 is an apocalyptic number.

It is an amenable number.

1551661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1551661 is an equidigital number, since it uses as much as digits as its factorization.

1551661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 900, while the sum is 25.

The square root of 1551661 is about 1245.6568548360. The cubic root of 1551661 is about 115.7707770269.

The spelling of 1551661 in words is "one million, five hundred fifty-one thousand, six hundred sixty-one".