20155661 has 8 divisors (see below), whose sum is σ = 20478744. Its totient is φ = 19835200.

The previous prime is 20155651. The next prime is 20155669. The reversal of 20155661 is 16655102.

It can be written as a sum of positive squares in 4 ways, for example, as 7123561 + 13032100 = 2669^2 + 3610^2 .

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 20155661 - 2¹⁴ = 20139277 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20155661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20155669) 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, 19391 + ... + 20403.

It is an arithmetic number, because the mean of its divisors is an integer number (2559843).

Almost surely, 2^20155661 is an apocalyptic number.

It is an amenable number.

20155661 is a deficient number, since it is larger than the sum of its proper divisors (323083).

20155661 is a wasteful number, since it uses less digits than its factorization.

20155661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1311.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 20155661 is about 4489.5056520735. The cubic root of 20155661 is about 272.1441574728.

The spelling of 20155661 in words is "twenty million, one hundred fifty-five thousand, six hundred sixty-one".