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 A352137 a(n) is the first start of a sequence of exactly n members of A175648 under the map k -> 3*k+4. 0
 21, 6, 155, 1111, 77635, 25877, 16392913, 78494323 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n), 3*a(n)+4, 3*(3*a(n)+4)+4, ..., 3^(n-1)*a(n)+2*3^(n-1)-2 are in A175648 but 3^n*a(n)+2*3^n-2 is not. LINKS Table of n, a(n) for n=1..8. EXAMPLE a(3) = 155 because 155, 3*155+4 = 469 and 3*469+4 = 1411 are in A175648 but 3*1411+4 = 4237 is not (155 = 5*31, 159 = 3*53, 469 = 7*67, 473 - 11*43, 1411 = 17*83, and 1415 = 5*283 are semiprimes, but 4241 is prime). MAPLE f:= proc(n) option remember; if numtheory:-bigomega(n)=2 and numtheory:-bigomega(n+4)=2 then 1 + procname(3*n+4) else 0 fi end proc: V:= Vector(7): count:= 0: for nn from 1 while count < 7 do v:= f(nn); if v > 0 and V[v] = 0 then count:= count+1; V[v]:= nn; fi od: convert(V, list); CROSSREFS Cf. A001358, A175648, A352132. Sequence in context: A358268 A351321 A040426 * A040425 A337422 A040424 Adjacent sequences: A352134 A352135 A352136 * A352138 A352139 A352140 KEYWORD nonn,more AUTHOR J. M. Bergot and Robert Israel, Mar 05 2022 STATUS approved

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Last modified April 19 15:03 EDT 2024. Contains 371794 sequences. (Running on oeis4.)