21780151 has 2 divisors, whose sum is σ = 21780152. Its totient is φ = 21780150.

The previous prime is 21780133. The next prime is 21780203. The reversal of 21780151 is 15108712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21780151 - 2¹⁷ = 21649079 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21789151) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10890075 + 10890076.

It is an arithmetic number, because the mean of its divisors is an integer number (10890076).

Almost surely, 2^21780151 is an apocalyptic number.

21780151 is a deficient number, since it is larger than the sum of its proper divisors (1).

21780151 is an equidigital number, since it uses as much as digits as its factorization.

21780151 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 560, while the sum is 25.

The square root of 21780151 is about 4666.9209335492. The cubic root of 21780151 is about 279.2674345465.

Adding to 21780151 its reverse (15108712), we get a palindrome (36888863).

The spelling of 21780151 in words is "twenty-one million, seven hundred eighty thousand, one hundred fifty-one".