A119689 Numbers n such that the sum of the largest distinct prime divisor and the smallest distinct prime divisor is a prime.

6, 10, 12, 18, 20, 22, 24, 30, 34, 36, 40, 44, 48, 50, 54, 58, 60, 66, 68, 72, 80, 82, 88, 90, 96, 100, 102, 108, 110, 116, 118, 120, 132, 136, 142, 144, 150, 154, 160, 162, 164, 170, 174, 176, 180, 192, 198, 200, 202, 204, 214, 216, 220, 232, 236, 238, 240, 242, 246

Offset

1,1

Comments

Also numbers whose largest prime divisor is the smaller part of a twin prime pair. - Stefan Steinerberger, Jul 22 2006

Empirical: all terms are even numbers. - Harvey P. Dale, Sep 22 2016

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

If n=6 then the largest and the smallest distinct prime divisors are 3 and 2 and their sum is a prime.
If n=90 then the largest and the smallest distinct prime divisors are 5 and 2 and their sum is a prime.

Mathematica

Select[Range[2, 500], PrimeQ[FactorInteger[ # ][[1, 1]] + FactorInteger[ # ][[ -1, 1]]] &] (* Stefan Steinerberger, Jul 22 2006 *)
pdQ[n_]:=Module[{f=FactorInteger[n][[All, 1]]}, PrimeQ[f[[1]]+f[[-1]]]]; Select[Range[2, 300], pdQ] (* Harvey P. Dale, Sep 22 2016 *)

Crossrefs

Cf. A119613.

Sequence in context: A316991 A316992 A262481 * A351614 A066038 A242100

Adjacent sequences: A119686 A119687 A119688 * A119690 A119691 A119692

Keyword

nonn

Author

Parthasarathy Nambi, Jun 09 2006

Extensions

More terms from Stefan Steinerberger, Jul 22 2006

Status

approved