Properties of the Number 21780

Twenty-One Thousand Seven Hundred Eighty

Basics

Value: 21779 → 21780 → 21781

Parity: even

Prime: No

Previous Prime: 21773

Next Prime: 21787

Digit Sum: 18

Digital Root: 9

Palindrome: No

Factorization: 2 ² × 3 ² × 5 × 11 ²

Divisors: 1, 2, 3, 4, 5, 6, 9, 10, 11, 12

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

2196 Try Today's Challenge

Representations

Binary: 101010100010100

Octal: 52424

Duodecimal: 10730

Hexadecimal: 5514

Square: 474368400

Square Root: 147.58048651498612

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Numbers k such that σ(φ(k)) = φ(σ(k)). A33632

Exponential abundant numbers: integers k for which A126164(k) > k, or equivalently for which A051377(k) > 2k. A129575

a(n) = n² * φ(n). A53191

Number of partitions of 2·n with no part divisible by 3 and all odd parts occurring with even multiplicities. A98151

Numbers k such that k and 4·k are anagrams. A23088

Numbers k such that 6·k+1, 6·k+7, 6·k+13, 6·k+19 are consecutive primes. A90839

a(n) = 20·n². A195322

Number of paraffins. A5997

Numbers that have exactly seven prime factors counted with multiplicity (A046308) whose digit reversal is different and also has 7 prime factors (with multiplicity). A109027

a(n) = n²*(2·n+1). A99721