21261955 has 32 divisors (see below), whose sum is σ = 30336768. Its totient is φ = 14102400.

The previous prime is 21261953. The next prime is 21261971. The reversal of 21261955 is 55916212.

21261955 = 384² + 385² + ... + 493².

It is not a de Polignac number, because 21261955 - 2¹ = 21261953 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21261953) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 93552 + ... + 93778.

It is an arithmetic number, because the mean of its divisors is an integer number (948024).

Almost surely, 2^21261955 is an apocalyptic number.

21261955 is a deficient number, since it is larger than the sum of its proper divisors (9074813).

21261955 is a wasteful number, since it uses less digits than its factorization.

21261955 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 387.

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

The square root of 21261955 is about 4611.0687481320. The cubic root of 21261955 is about 277.0348455427.

It can be divided in two parts, 21 and 261955, that multiplied together give a palindrome (5501055).

The spelling of 21261955 in words is "twenty-one million, two hundred sixty-one thousand, nine hundred fifty-five".