Voozh

A378172

Numbers m such that k = 4*m is powerful while both 4*m-1 and 4*m+1 are squarefree.

1, 4, 8, 9, 18, 27, 32, 36, 49, 50, 54, 64, 98, 100, 108, 121, 125, 162, 216, 225, 242, 243, 288, 289, 324, 338, 343, 392, 400, 432, 441, 450, 486, 500, 512, 648, 675, 676, 729, 784, 800, 841, 864, 882, 900, 1000, 1058, 1089, 1125, 1152, 1250, 1296, 1323, 1350

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 1, k = 4, since both 3 and 5 are prime and thus squarefree.

2 is not in the sequence since 4*2+1 = 9 is not squarefree.

a(2) = 4, k = 16 since both 15 and 17 are squarefree.

a(3) = 8, k = 32, since both 31 and 33 are squarefree.

a(4) = 9, k = 36, since both 35 and 37 are squarefree.

16 is not in the sequence since 16*4-1 = 63 = 3^2*7 is not squarefree, etc.