1661261281 has 8 divisors (see below), whose sum is σ = 1672544160. Its totient is φ = 1649992032.

The previous prime is 1661261279. The next prime is 1661261291. The reversal of 1661261281 is 1821621661.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1661261281 - 2¹ = 1661261279 is a prime.

It is a super-2 number, since 2×1661261281² = 5519578087499521922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661261291) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 387930 + ... + 392188.

It is an arithmetic number, because the mean of its divisors is an integer number (209068020).

Almost surely, 2^1661261281 is an apocalyptic number.

It is an amenable number.

1661261281 is a deficient number, since it is larger than the sum of its proper divisors (11282879).

1661261281 is a wasteful number, since it uses less digits than its factorization.

1661261281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6815.

The product of its digits is 6912, while the sum is 34.

The square root of 1661261281 is about 40758.5730981839. The cubic root of 1661261281 is about 1184.3479546422.

The spelling of 1661261281 in words is "one billion, six hundred sixty-one million, two hundred sixty-one thousand, two hundred eighty-one".