A080863 Numbers n such that spf(n)-2 = spf(n+2), where spf=A020639 (smallest prime factor).

25, 55, 85, 115, 145, 175, 203, 205, 235, 265, 295, 325, 355, 385, 413, 415, 445, 475, 505, 535, 565, 595, 623, 625, 655, 685, 715, 745, 775, 805, 833, 835, 865, 895, 925, 955, 985, 1015, 1043, 1045, 1075, 1105, 1135, 1165, 1195, 1225, 1253, 1255, 1285

Offset

1,1

Comments

(spf(n+2),spf(n)) are twin prime pairs.

Links

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

Example

16151=31*521, 16151+2=16153=29*557 and (29,31)=(A001359(5), A006512(5)), therefore 16151 is a term: a(625)=16151, A080864(625)=16153.

Mathematica

Flatten[Position[Partition[Table[FactorInteger[n][[1, 1]], {n, 1300}], 3, 1], _?(#[[1]]-2==#[[3]]&), {1}, Heads->False]] (* Harvey P. Dale, Mar 07 2016 *)

Crossrefs

Cf. A080864(n)=a(n)+2, A001359, A006512.

Sequence in context: A276448 A176275 A108166 * A339729 A091214 A338009

Adjacent sequences: A080860 A080861 A080862 * A080864 A080865 A080866

Keyword

nonn

Author

Reinhard Zumkeller, Feb 21 2003

Status

approved