20551 has 2 divisors, whose sum is σ = 20552. Its totient is φ = 20550.

The previous prime is 20549. The next prime is 20563. The reversal of 20551 is 15502.

20551 = 56² + 57² + ... + 61².

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20551 - 2¹ = 20549 is a prime.

Together with 20549, it forms a pair of twin primes.

20551 is a lucky number.

It is a nialpdrome in base 12.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10275 + 10276.

It is an arithmetic number, because the mean of its divisors is an integer number (10276).

2²⁰⁵⁵¹ is an apocalyptic number.

20551 is a deficient number, since it is larger than the sum of its proper divisors (1).

20551 is an equidigital number, since it uses as much as digits as its factorization.

20551 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 50, while the sum is 13.

The square root of 20551 is about 143.3561997264. The cubic root of 20551 is about 27.3911954235.

It can be divided in two parts, 205 and 51, that added together give a 8-th power (256 = 2⁸).

The spelling of 20551 in words is "twenty thousand, five hundred fifty-one".