WON plate80 | World!OfNumbers  Some curious polygonals The 44th enneagonal (9-sided polygonal) number is 6666 ! (Sloane's A028992) The 26th decagonal (10-sided polygonal) number is 2626 ! (Sloane's A001107) The 74th heptagonal (7-sided polygonal : n[5n-3]) number is 13579 (Sloane's A014637), a number with its odd digits in ascending order ! Variations on the theme : %N n^2 has digits in ascending order. under A028819 %N Squares with digits in ascending order. under A028820 %N n^2 has digits in descending order. under A028821 %N Squares with digits in descending order. under A028822 %N Primes with digits in ascending order. under A028864 %N Primes with digits in descending order. under A028867 %N Primes that when squared gives numbers with digits in ascending order. under A028865 %N Primes that when squared gives numbers with digits in descending order. under A028868 %N Squares of primes with digits in ascending order. under A028866 %N Squares of primes with digits in descending order. under A028869  A000080 Prime Curios! Prime Puzzle  Wikipedia 80 Le Nombre 80 Numberland 80 ```

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Patrick De Geest - Belgium - Short Bio - Some Pictures