A157485 Numbers k such that k-+1 are divisible by exactly 5 primes, counted with multiplicity.

271, 593, 701, 751, 919, 1169, 1241, 1639, 1649, 1673, 1711, 1751, 2071, 2311, 2393, 2549, 2551, 2609, 2729, 2861, 2863, 2897, 2899, 3185, 3331, 3569, 3631, 3823, 3849, 3851, 3943, 3977, 4231, 4265, 4649, 4663, 5071, 5081, 5237, 5239, 5391, 5551, 5561, 5585, 5741

Offset

1,1

Links

Jinyuan Wang, Table of n, a(n) for n = 1..5000

Mathematica

q=5; lst={}; Do[If[Plus@@Last/@FactorInteger[n-1]==q&&Plus@@Last/@FactorInteger[n+1]==q, AppendTo[lst, n]], {n, 7!}]; lst
Select[Range[6000], PrimeOmega[#+{1, -1}]=={5, 5}&] (* Harvey P. Dale, Jun 05 2021 *)
Mean/@SequencePosition[PrimeOmega[Range[6000]], {5, _, 5}] (* Harvey P. Dale, Oct 19 2023 *)

Prog

(PARI) is(k) = bigomega(k-1)==5 && bigomega(k+1)==5; \\ Jinyuan Wang, Mar 22 2020

Crossrefs

Cf. A014612, A124936, A157483, A157484.

Sequence in context: A142637 A288881 A245969 * A038655 A108835 A185668

Adjacent sequences: A157482 A157483 A157484 * A157486 A157487 A157488

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Mar 01 2009

Extensions

More terms from Jinyuan Wang, Mar 22 2020

Status

approved