A157487 Numbers k such that k-1 and k+1 are each the product of exactly 7 primes, counted with multiplicity.

10529, 15391, 17983, 18751, 22049, 23489, 24751, 26081, 29249, 32561, 35153, 43471, 49951, 52975, 58049, 58481, 67229, 67231, 70687, 71873, 72415, 76049, 77921, 79001, 79649, 82783, 83249, 85751, 88289, 93799, 95551, 97471, 102545

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Mar 01 2009

Keywords

• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..3000

Crossrefs

Cf. A124936, A014612, A157483, A157484, A157485, A157486.

Programs

Maple

with(numtheory): a := proc (n) if bigomega(n-1) = 7 and bigomega(n+1) = 7 then n else end if end proc: seq(a(n), n = 2 .. 120000); # Emeric Deutsch, Mar 07 2009

Mathematica

q=7;lst={};Do[If[Plus@@Last/@FactorInteger[n-1]==q&&Plus@@Last/@FactorInteger[n+1]==q,AppendTo[lst,n]],{n,9!}];lst
Select[Range[110000],PrimeOmega[#+{1,-1}]=={7,7}&] (* Harvey P. Dale, Apr 04 2015 *)
Mean/@SequencePosition[PrimeOmega[Range[105000]],{7,,7}] (* _Harvey P. Dale, Sep 10 2022 *)

Extensions

More terms from Emeric Deutsch, Mar 07 2009