A380913 Squarefree semiprimes that are centered triangular numbers.
10, 46, 85, 166, 235, 274, 514, 694, 901, 1135, 1219, 1306, 1585, 1891, 2461, 2839, 3106, 3385, 3826, 3979, 4135, 5311, 5674, 6049, 6835, 7246, 8551, 9481, 10966, 11485, 11749, 12286, 12559, 13969, 15151, 15454, 17335, 18649, 18985, 19666, 21421, 21781, 22879, 23626
Offset: 1
Keywords
Examples
10 = 2 * 5 which is the 3rd centered triangular number. 46 = 2 * 23 which is the 6th centered triangular number. 85 = 5 * 17 which is the 7th centered triangular number.
Programs
-
Mathematica
Select[Table[3*n*(n-1)/2 + 1, {n, 1, 130}], FactorInteger[#][[;; , 2]] == {1, 1} &] (* Amiram Eldar, Feb 08 2025 *)
Comments