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

1,1

Links

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

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 *)

Crossrefs

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

Sequence in context: A216489 A120500 A371623 * A203666 A346892 A119866

Adjacent sequences: A157484 A157485 A157486 * A157488 A157489 A157490

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Mar 01 2009

Extensions

More terms from Emeric Deutsch, Mar 07 2009

Status

approved