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A136048 Semiprime terms in A136047. 3
185, 497, 511, 1041, 1059, 1903, 3107, 4705, 4735, 6817, 9481, 12761, 16721, 33379, 48961, 49027, 68857, 80561, 80639, 93521, 179503, 201241, 250097, 306281, 306403, 405551, 482161, 482303, 523921, 885631, 947939, 1081001, 1081187, 1226177 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

185 = 5*37, 497 = 7*71, 511 = 7*73, 1041 = 3*347, 1059 = 3*353, 1903 = 11*173, 3107 = 13*239, 4705 = 5*941, 4735 = 5*947, 6817 = 17*401, 9481 = 19*499, 12761 = 7*1823, 16721 = 23*727, 33379 = 29*1151, 48961 = 11*4451, 49027 = 11*4457, 68857 = 37*1861, 80561 = 13*6197, 80639 = 13*6203, 93521 = 41*2281.

Positions of a(n) in A136047 are given in A135439.

LINKS

Table of n, a(n) for n=1..34.

MATHEMATICA

a[1]=1; a[n_]:=a[n]=a[n-1]+n^(1+Mod[n, 2]); A136047=Table[a[n], {n, 1000}]; A136048=Select[A136047, Total[Last/@FactorInteger[ # ]]==2&]

nxt[{n_, a_}]:={n+1, If[OddQ[n], a+n+1, a+(n+1)^2]}; Select[ Transpose[ NestList[ nxt, {1, 1}, 200]][[2]], PrimeOmega[#]==2&] (* Harvey P. Dale, Oct 11 2015 *)

CROSSREFS

Cf. A136047.

Sequence in context: A252272 A247529 A301991 * A209373 A207076 A189181

Adjacent sequences:  A136045 A136046 A136047 * A136049 A136050 A136051

KEYWORD

nonn

AUTHOR

Zak Seidov, Dec 12 2007

STATUS

approved

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Last modified September 24 07:28 EDT 2020. Contains 337317 sequences. (Running on oeis4.)