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A330597
Squarefree numbers in which all substrings are squarefree.
1
1, 2, 3, 5, 6, 7, 11, 13, 15, 17, 21, 22, 23, 26, 31, 33, 35, 37, 51, 53, 55, 57, 61, 62, 65, 66, 67, 71, 73, 77, 111, 113, 115, 131, 133, 137, 151, 155, 157, 173, 177, 211, 213, 215, 217, 221, 222, 223, 226, 231, 233, 235, 237, 262, 265, 266, 267, 311, 313
OFFSET
1,2
COMMENTS
This sequence is finite, the last term being a(1690) = 77377717.
LINKS
EXAMPLE
1, 3, 7, 13, 37 and 137 are all squarefree, hence 137 is a term.
MATHEMATICA
sfQ[k_]:=With[{i=IntegerDigits[k]}, AllTrue[Flatten[Table[ FromDigits/@ Partition[ i, n, 1], {n, IntegerLength[k]}]], SquareFreeQ]]; Select[ Range[ 350], sfQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 09 2020 *)
PROG
(PARI) See Links section.
CROSSREFS
Cf. A005117, A085823 (prime variant), A202262 (composite variant).
Sequence in context: A098962 A073485 A062101 * A352336 A283599 A096530
KEYWORD
nonn,base,fini,full
AUTHOR
Rémy Sigrist, Dec 19 2019
STATUS
approved