OFFSET
1,1
COMMENTS
Sphenic numbers are numbers that are products of three distinct primes.
This sequence is different from A362811: sphenic numbers sandwiched between semiprimes, as semiprimes are products of two primes that might not be distinct.
EXAMPLE
186 = 2*3*31 is a sphenic number sandwiched between 185 = 5*37 and 187 = 11*17, both of which are squarefree semiprimes. Thus, 186 is in this sequence.
290 = 2*5*29 is a sphenic number sandwiched between semiprimes 289 = 17*17 and 291 = 3*97, one of which is not squarefree. Thus, 290 is not in this sequence but in A362811.
MATHEMATICA
Select[Range[4000], Transpose[FactorInteger[#]][[2]] == {1, 1, 1} && Transpose[FactorInteger[# - 1]][[2]] == {1, 1} && Transpose[FactorInteger[# + 1]][[2]] == {1, 1} &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Tanya Khovanova and Massimo Kofler, Jun 14 2023
STATUS
approved