1661561005 has 16 divisors (see below), whose sum is σ = 2182454064. Its totient is φ = 1206881280.

The previous prime is 1661560993. The next prime is 1661561021. The reversal of 1661561005 is 5001651661.

It can be written as a sum of positive squares in 8 ways, for example, as 365344996 + 1296216009 = 19114^2 + 36003^2 .

It is not a de Polignac number, because 1661561005 - 2¹³ = 1661552813 is a prime.

It is a super-2 number, since 2×1661561005² = 5521569946673220050, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 205564 + ... + 213493.

It is an arithmetic number, because the mean of its divisors is an integer number (136403379).

Almost surely, 2^1661561005 is an apocalyptic number.

It is an amenable number.

1661561005 is a deficient number, since it is larger than the sum of its proper divisors (520893059).

1661561005 is a wasteful number, since it uses less digits than its factorization.

1661561005 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 419136.

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

The square root of 1661561005 is about 40762.2497539083. The cubic root of 1661561005 is about 1184.4191768644.

The spelling of 1661561005 in words is "one billion, six hundred sixty-one million, five hundred sixty-one thousand, five".