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

Author

Vladimir Joseph Stephan Orlovsky, Mar 01 2009

Keywords

• nonn

Links

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

Crossrefs

Cf. A014612, A124936, A157483, A157484.

Programs

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 *)

PARI

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

Extensions

More terms from Jinyuan Wang, Mar 22 2020