A073249 Nonprime squarefree numbers n such that both n-1 and n+1 are not squarefree and not prime.

26, 51, 55, 91, 161, 170, 235, 249, 295, 305, 339, 341, 362, 377, 413, 415, 451, 485, 489, 530, 551, 559, 579, 595, 629, 638, 649, 651, 665, 667, 685, 687, 703, 721, 723, 737, 749, 849, 851, 874, 917, 926, 949, 951, 955, 962, 989, 1015, 1027, 1057, 1059

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

npsQ[n_]:=SquareFreeQ[n]&&NoneTrue[n+{1, 0, -1}, PrimeQ]&&NoneTrue[n+{1, -1}, SquareFreeQ]; Select[Range[2000], npsQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 20 2019 *)
Mean/@SequencePosition[Table[Which[CompositeQ[n]&&SquareFreeQ[n], 1, !SquareFreeQ[ n] && CompositeQ[ n], -1, True, 0], {n, 1100}], {-1, 1, -1}] (* Harvey P. Dale, Jun 17 2022 *)

Crossrefs

Cf. A000469, A005117, A073247, A073250, A073251.

Sequence in context: A364025 A324041 A137263 * A044078 A044459 A158060

Adjacent sequences: A073246 A073247 A073248 * A073250 A073251 A073252

Keyword

nonn

Author

Reinhard Zumkeller, Jul 22 2002

Extensions

Corrected by Harvey P. Dale, Jan 20 2019

Status

approved