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A157487 Numbers k such that k-1 and k+1 are each the product of exactly 7 primes, counted with multiplicity. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
Sequence in context: A236036 A216489 A120500 * A203666 A346892 A119866
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Emeric Deutsch, Mar 07 2009
STATUS
approved

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Last modified April 16 05:35 EDT 2024. Contains 371697 sequences. (Running on oeis4.)