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A179679 Smaller of each pair of consecutive primes which sum to a practical number. 0

%I #6 Jul 14 2015 01:09:53

%S 3,5,7,11,13,17,19,29,37,41,43,47,53,59,61,71,79,97,101,103,107,113,

%T 137,139,149,151,157,163,167,173,179,191,193,197,223,227,229,239,257,

%U 263,269,277,283,293,311,313,317,337,347,349,359,367,397,401,409,419,431

%N Smaller of each pair of consecutive primes which sum to a practical number.

%C Complement is: 2, 23, 31, 67, 73, 83, 89, 109, 127, 131, 181, 199, 211, ..., . - _Robert G. Wilson v_, Aug 03 2010

%e 19 is a term because the next consecutive prime is 23, and 19 + 23 = 42, which is a practical number.

%t PracticalQ[n_] := Module[{f, p, e, prod = 1, ok = True}, If[n < 1 || (n > 1 && OddQ[n]), False, If[n == 1, True, f = FactorInteger[n]; {p, e} = Transpose[f]; Do[If[p[[i]] > 1 + DivisorSigma[1, prod], ok = False; Break[]]; prod = prod*p[[i]]^e[[i]], {i, Length[p]}]; ok]]]; First@# & /@ Select[ Partition[ Prime@ Range@ 85, 2, 1], PracticalQ[Plus @@ # ] &] (* _Robert G. Wilson v_, Aug 03 2010 *)

%Y Cf. A000040, A005153.

%K nonn

%O 1,1

%A _Jason G. Wurtzel_, Jul 24 2010

%E More terms from _Robert G. Wilson v_, Aug 03 2010

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Last modified March 19 06:05 EDT 2024. Contains 370952 sequences. (Running on oeis4.)