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

3, 5, 7, 11, 13, 17, 19, 29, 37, 41, 43, 47, 53, 59, 61, 71, 79, 97, 101, 103, 107, 113, 137, 139, 149, 151, 157, 163, 167, 173, 179, 191, 193, 197, 223, 227, 229, 239, 257, 263, 269, 277, 283, 293, 311, 313, 317, 337, 347, 349, 359, 367, 397, 401, 409, 419, 431

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..57.

Example

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

Mathematica

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 *)

Crossrefs

Cf. A000040, A005153.

Sequence in context: A239879 A001097 A117243 * A059362 A212376 A059264

Adjacent sequences: A179676 A179677 A179678 * A179680 A179681 A179682

Keyword

nonn

Author

Jason G. Wurtzel, Jul 24 2010

Extensions

More terms from Robert G. Wilson v, Aug 03 2010

Status

approved