OFFSET
1,1
COMMENTS
Equivalently, smallest prime p such that p+1 is an n-almost prime. For smallest prime p such that p+1 is a squarefree n-almost prime, see A098026.
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 1..421
EXAMPLE
a(4) = 23 because 23 is prime and 23+1 = 2*2*2*3 has 4 prime factors (24 is a 4-almost prime).
MATHEMATICA
(* copied directly from A073919 with only a sign change *) ptns[n_, 0] := If[n==0, {{}}, {}]; ptns[n_, k_] := Module[{r}, If[n<k, Return[{}]]; ptns[n, k] = 1 + Union@@ Table[ PadRight[ #, k] &/ @ ptns[n-k, r], {r, 0, k}]]; a[n_] := Module[{i, l, v}, v=Infinity; For[i=n, True, i++, l=(Times@@ Prime /@ # &)/@ ptns[i, n]; If[ Min @@ l > v, Return[v]]; minp = Min@@ Select[l - 1, ProvablePrimeQ]; If[minp < v, v = minp]]] (* First do <<NumberTheory`PrimeQ`. ptns[n, k] is list of partitions of n into exactly k parts *) (* appended by Robert G. Wilson v *) Array[a, 32] (* Robert G. Wilson v, Jul 21 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, May 03 2006
EXTENSIONS
a(26)-a(32) from Donovan Johnson, Feb 02 2011
STATUS
approved