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 A133597 Array of semiprimes, read by antidiagonals, where row k is the first of pairs of consecutive semiprimes j and j+k. 0
 9, 4, 14, 6, 49, 21, 10, 22, 55, 25, 69, 51, 35, 91, 33, 15, 77, 58, 46, 119, 34, 26, 123, 106, 65, 62, 143, 38, 169, 39, 365, 161, 87, 74, 159, 57, 146, 437, 134, 371, 178, 111, 82, 183, 85, 237, 226, 458, 187, 505, 221, 129, 115, 185, 86 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Every semiprime occurs in this table exactly once. Note that similar tables exist for k-almost primes (integers with exactly k prime factors, with multiplicity), this being the k=2 slice of a 3-dimensional array. LINKS Table of n, a(n) for n=1..55. EXAMPLE The array begins: ================================================================== n=......1....2.....3....4....5....6....7....8....9...10 ================================================================== k=1.|...9...14....21...25...33...34...38...57...85...86....A070552 k=2.|...4...49....55...91..119..143..159..183..185..203....A136196 k=3.|...6...22....35...46...62...74...82..115..155..166....A264043 k=4.|. 10...51....58...65...87..111..129..209..249..274....A264044 k=5.|..69...77...106..161..178..221..254..309..314..329....A264045 k=6.|..15..123...365..371..505..545..573..591..649..707....A264046 k=7.|..26...39...134..187..194..267..519..566..655..771.... k=8.|.169..437...458..614..723..737..905..965.1047.1059.... k=9.|.146..226...278..346.1018.1177.1273.1546.1594.1865.... k=10|.237..427..1027.1101.1661.2723.2747.3173.3295.3669....A217030 ================================================================== MATHEMATICA v = Select[Range[5000], PrimeOmega[#]==2 &]; L[k_] := L[k] = v[[Select[Range[Length[v]-1], v[[#+1]] - v[[#]] == k &]]]; Flatten@ Table[ Table[L[k-j+1][[j]], {j, k}], {k, 10}] (* Giovanni Resta, Jun 20 2016 *) CROSSREFS Cf. A001358, A070552, A136196. Sequence in context: A153698 A168203 A248310 * A075066 A061363 A100077 Adjacent sequences: A133594 A133595 A133596 * A133598 A133599 A133600 KEYWORD easy,nonn,tabl AUTHOR Jonathan Vos Post, Dec 27 2007 EXTENSIONS Corrected and edited by Giovanni Resta, Jun 20 2016 STATUS approved

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Last modified September 16 07:48 EDT 2024. Contains 375959 sequences. (Running on oeis4.)