A276050 Isolated deficient numbers that are composite.

55, 161, 175, 209, 221, 259, 305, 319, 341, 351, 365, 391, 415, 475, 497, 533, 545, 551, 559, 581, 649, 679, 703, 737, 749, 785, 799, 833, 835, 869, 895, 979, 1001, 1037, 1099, 1121, 1145, 1147, 1159, 1183, 1189, 1205, 1219, 1241, 1313, 1315, 1331, 1339, 1351, 1375, 1421, 1457, 1495

Offset

1,1

Comments

Deficient composite numbers a(n) for which a(n)-1 and a(n)+1 are not deficient. In most instances, both a(n)-1 and a(n)+1 will be abundant numbers; in a few instances, one will be abundant while the other one is perfect.

Links

Timothy L. Tiffin, Table of n, a(n) for n = 1..223 [terms up to 5000]

Example

55 = 5*11 is between two abundant numbers (54 and 56), while 497 = 7*71 is between a perfect number (496) and an abundant number (498).

Mathematica

Select[Range@ 1500, And[CompositeQ@ #, Boole@ Map[DivisorSigma[1, #] < 2 # &, # + Range[-1, 1]] == {0, 1, 0}] &] (* Michael De Vlieger, Aug 26 2016 *)

Crossrefs

Subsequence of both A005100 and A274849, complement of A276049 in A274849.

Sequence in context: A044387 A044768 A352268 * A256353 A068641 A039781

Adjacent sequences: A276047 A276048 A276049 * A276051 A276052 A276053

Keyword

nonn

Author

Timothy L. Tiffin, Aug 17 2016

Status

approved