A144158 - OEIS

%I #8 Oct 05 2015 02:57:09

%S 2,18,16,150,42,112,81,40,605,48,507,196,225,128,5202,12,7220,20,441,

%T 484,12696,18,250,676,243,112,5887,180,4805,320,1089,1156,1225,144,

%U 222,2812,2223,1040,615,3444,903,3784,990,30,2116,106032,24,686,500,306

%N (1=1, 2=2, 3=3, 4=2^2, 5=5, 6=2*3, 7=7, 8=2^3, 9=3^2, 10=2*5, 11=11, 12=2^2*3, 13=13, ...) becomes (1*1*2, 2*3*3, 4*2*2, 5*5*6, 2*3*7, 7*8*2, 3*9*3, 2*10*2, 5*11*11, 12*2*2, 3*13*13, ...).

%e 3*13*13 = 507 = a(11),

%e 14*2*7 = 196 = a(12),

%e 15*3*5 = 225 = a(13),

%e 16*2*4 = 128 = a(14),

%e 17*17*18 = 5202 = a(15),

%e 2*3*2 = 12 = a(16),

%e 19*19*20 = 7220 = a(17),

%e etc.

%p pflat := proc(nmax) local a, ifs, n, p, c ; a := [1,1] ; for n from 2 to nmax do a := [op(a),n] ; ifs := ifactors(n)[2] ; for p in ifs do a := [op(a),op(1,p)] ; if op(2,p) > 1 then a := [op(a),op(2,p)] ; fi; od: od: a ; end: L := pflat(300) ; for n from 1 to nops(L)-3 by 3 do printf("%d,", op(n,L)*op(n+1,L)*op(n+2,L) ) ; end do: # _R. J. Mathar_, Apr 29 2010

%Y Cf. A141186, A136740, A136811, A143717.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Nov 17 2008

%E a(37) and terms after a(46) corrected by _R. J. Mathar_, Apr 29 2010