A117369 a(n) = smallest prime which is > smallest prime dividing n and is coprime to n.

2, 3, 5, 3, 7, 5, 11, 3, 5, 3, 13, 5, 17, 3, 7, 3, 19, 5, 23, 3, 5, 3, 29, 5, 7, 3, 5, 3, 31, 7, 37, 3, 5, 3, 11, 5, 41, 3, 5, 3, 43, 5, 47, 3, 7, 3, 53, 5, 11, 3, 5, 3, 59, 5, 7, 3, 5, 3, 61, 7, 67, 3, 5, 3, 7, 5, 71, 3, 5, 3, 73, 5, 79, 3, 7

Offset

1,1

Links

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

Example

a(6) = 5 because 5 is the smallest prime which is both greater than the smallest prime dividing 6, which is 2 and is coprime to 6.

Mathematica

a[1] := 2; a[n_] := Module[{}, k = PrimePi[FactorInteger[n][[1, 1]]]; k++; While[Not[GCD[Prime[k], n] == 1 ], k++ ]; Prime[k]]; Table[a[i], {i, 1, 80}] (* Stefan Steinerberger and Patrick Hanslmaier, Jun 03 2007 *)
spdn[n_]:=Module[{s=FactorInteger[n][[1, 1]], p}, p=NextPrime[s]; While[ !CoprimeQ[ p, n], p=NextPrime[p]]; p]; Array[spdn, 80] (* Harvey P. Dale, Feb 18 2018 *)

Crossrefs

Cf. A079068, A117367.

Sequence in context: A080184 A052248 A092386 * A117366 A341643 A073482

Adjacent sequences: A117366 A117367 A117368 * A117370 A117371 A117372

Keyword

nonn

Author

Leroy Quet, Mar 10 2006

Extensions

More terms from Stefan Steinerberger and Patrick Hanslmaier, Jun 03 2007

Status

approved