21551365 has 16 divisors (see below), whose sum is σ = 28558656. Its totient is φ = 15481600.

The previous prime is 21551357. The next prime is 21551401. The reversal of 21551365 is 56315512.

21551365 = T₁₉₇₄ + T₁₉₇₅ + ... + T₁₉₈₄.

21551365 = 468² + 469² + ... + 550².

It is not a de Polignac number, because 21551365 - 2³ = 21551357 is a prime.

It is a super-2 number, since 2×21551365² = 928922666726450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2205 + ... + 6925.

It is an arithmetic number, because the mean of its divisors is an integer number (1784916).

Almost surely, 2^21551365 is an apocalyptic number.

It is an amenable number.

21551365 is a deficient number, since it is larger than the sum of its proper divisors (7007291).

21551365 is a wasteful number, since it uses less digits than its factorization.

21551365 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4820.

The product of its digits is 4500, while the sum is 28.

The square root of 21551365 is about 4642.3447739262. The cubic root of 21551365 is about 278.2861510215.

Adding to 21551365 its reverse (56315512), we get a palindrome (77866877).

The spelling of 21551365 in words is "twenty-one million, five hundred fifty-one thousand, three hundred sixty-five".