A242066 The smallest even k such that lpf_3(k-3) > lpf_3(k-1) >= p_n, where lpf_3(n) = lpf(n/3^t) (cf. A020639) such that 3^t (t>=0) is the maximal power of 3 which divides n.

16, 22, 34, 40, 70, 70, 70, 112, 112, 112, 130, 130, 142, 160, 184, 184, 202, 214, 310, 310, 310, 310, 310, 310, 310, 340, 340, 340, 382, 412, 412, 490, 490, 490, 490, 490, 502, 544, 544, 544, 574, 580, 634, 634, 634, 754, 754, 754, 754, 754, 754, 754, 772

Offset

3,1

Comments

a(n)-3 and (a(n)-1)/3 are primes.

Links

Table of n, a(n) for n=3..55.

Mathematica

lpf[n_]:=lpf[n]=First[First[FactorInteger[n]]]; (*least prime factor*)
lpf3[n_]:=lpf3[n]=If[#==1, 1, lpf[#]]&[n/3^IntegerExponent[n, 3]];
Table[NestWhile[#+2&, 2, !(lpf3[#-3]>lpf3[#-1]>=Prime[n])&], {n, 3, 100}] (* Peter J. C. Moses, Aug 14 2014 *)

Crossrefs

Cf. A242057, A242058, A242059, A242060, A242064, A242065, A242033, A242034, A242036, A242037.

Sequence in context: A059756 A242214 A242559 * A303958 A304601 A165338

Adjacent sequences: A242063 A242064 A242065 * A242067 A242068 A242069

Keyword

nonn

Author

Vladimir Shevelev, Aug 13 2014

Status

approved