Search a number
BaseRepresentation
bin101010010011101
31002201021
411102131
51143121
6244141
7120103
oct52235
932637
1021661
1115302
1210651
139b23
147c73
156641
hex549d

21661 has 2 divisors, whose sum is σ = 21662. Its totient is φ = 21660.

The previous prime is 21649. The next prime is 21673. The reversal of 21661 is 16612.

It is a balanced prime because it is at equal distance from previous prime (21649) and next prime (21673).

It can be written as a sum of positive squares in only one way, i.e., 16900 + 4761 = 130^2 + 69^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661 - 29 = 21149 is a prime.

It is a nialpdrome in base 15.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830 + 10831.

It is an arithmetic number, because the mean of its divisors is an integer number (10831).

221661 is an apocalyptic number.

It is an amenable number.

21661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661 is an equidigital number, since it uses as much as digits as its factorization.

21661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72, while the sum is 16.

The square root of 21661 is about 147.1767644705. The cubic root of 21661 is about 27.8757247427.

The spelling of 21661 in words is "twenty-one thousand, six hundred sixty-one".