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A088986 Numbers n such that each of n through n+4 are divisible by exactly two primes. 1
54, 91, 92, 115, 141, 142, 143, 144, 158, 205, 212, 213, 214, 215, 295, 301, 323, 324, 325, 391, 535, 685, 721, 799, 1135, 1345, 1465, 1535, 1711, 1941, 1981, 2101, 2215, 2302, 2303, 2304, 2425, 2641, 3865, 4411, 5461, 6505, 6625, 6925, 7165, 7231, 7261 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Identical with A045933 from first-to 38th terms, but deviates later because A045933 includes start of chains with more than 2 prime-factors.

Contrary to longer chains(6,7,8,..) of omega=2 this sequence seems to be either infinite or very long. See A088963-A088985.

Primes counted without multiplicity. [Harvey P. Dale, Oct 20 2011]

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..750

MATHEMATICA

Transpose[Select[Partition[Transpose[Select[Table[{n, PrimeNu[n]}, {n, 10000}], Last[#]==2&]][[1]], 5, 1], Last[#]-First[#]==4&]][[1]] (* Harvey P. Dale, Oct 20 2011 *)

PROG

(Python)

from sympy import primefactors

def ok(n):

    return all(len(primefactors(n + i))==2 for i in range(5))

print([n for n in range(1, 8001) if ok(n)]) # Indranil Ghosh, Jul 17 2017

CROSSREFS

Sequence in context: A290146 A071863 A045933 * A259717 A118150 A039779

Adjacent sequences:  A088983 A088984 A088985 * A088987 A088988 A088989

KEYWORD

nonn

AUTHOR

Labos Elemer, Sep 30 2003

STATUS

approved

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Last modified October 26 02:14 EDT 2021. Contains 348256 sequences. (Running on oeis4.)