Properties of the Number 21781

Twenty-One Thousand Seven Hundred Eighty-One

Basics

Value: 21780 → 21781 → 21782

Parity: odd

Prime: No

Previous Prime: 21773

Next Prime: 21787

Digit Sum: 19

Digital Root: 1

Palindrome: No

Factorization: 23 × 947

Divisors: 1, 23, 947, 21781

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

2196 Try Today's Challenge

Representations

Binary: 101010100010101

Octal: 52425

Duodecimal: 10731

Hexadecimal: 5515

Square: 474411961

Square Root: 147.58387445788242

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

a(n) = 20·n² + 1. A158493

Pseudoprimes to base 17. A20145

Numbers n such that Q(sqrt(n)) has class number 9. A218041

Decimal representation of the x-axis, from the origin to the right edge, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 155", based on the 5-celled von Neumann neighborhood. A279253

Decimal representation of the x-axis, from the left edge to the origin, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 179", based on the 5-celled von Neumann neighborhood. A279666

Decimal representation of the x-axis, from the left edge to the origin, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 195", based on the 5-celled von Neumann neighborhood. A279750

Decimal representation of the x-axis, from the left edge to the origin, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 219", based on the 5-celled von Neumann neighborhood. A279957

Decimal representation of the x-axis, from the origin to the right edge, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 324", based on the 5-celled von Neumann neighborhood. A281105

a(n) = (27·n² + 9·n + 2)/2. A93485

Triangle T(n,k) read by rows: T(n,1) = T(n,n)=1, otherwise T(n,k) = (3n-3k+1)*T(n-1,k-1) + k*(3k-2)*T(n-1,k), 1<=k<=n. A166962