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A331802
Integers having no representation as sum of two nonsquarefree numbers.
1
1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 14, 15, 19, 23
OFFSET
1,2
COMMENTS
This sequence is finite with 14 terms and 23 is the largest term (see Prime Curios link); a proof can be found in comments of A331801.
LINKS
G. L. Honaker, Jr. and Chris K. Caldwell, Prime Curios! 23
EXAMPLE
With the two smallest nonsquarefree numbers 4 and 8, it is not possible to get 1, 2, 3, 4, 5, 6, 7, 9, 10 and 11 as sum of two nonsquarefree numbers.
MATHEMATICA
max = 25; Complement[Range[max], Union @ Select[Total /@ Tuples[Select[Range[max], !SquareFreeQ[#] &], 2], # <= max &]] (* Amiram Eldar, Feb 24 2020 *)
CROSSREFS
Cf. A005117 (squarefree), A013929 (nonsquarefree), A331801 (complement).
Cf. A000404 (sum of 2 nonzero squares), A018825 (not the sum of 2 nonzero squares).
Cf. A001694 (squareful), A052485 (not squareful), A076871 (sum of 2 squareful), A085253 (not the sum of 2 squareful).
Sequence in context: A272570 A123101 A071557 * A271108 A179401 A117729
KEYWORD
nonn,full,fini
AUTHOR
Bernard Schott, Feb 23 2020
STATUS
approved