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

Author

Vladimir Shevelev, Aug 13 2014

Keywords

• nonn

Comments

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

Crossrefs

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

Programs

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 *)