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 A176658 Numbers k such that semiprime(semiprime(k)) + 1 = semiprime(semiprime(k+1)). 0

%I

%S 3,5,11,14,20,32,52,57,70,72,81,95,114,124,231,240,273,276,287,291,

%T 371,380,441,507,528,544,573,607,629,647,672,695,716,739,828,830,832,

%U 873,1002,1035,1037,1044,1100,1104,1182,1208,1236,1278,1321,1340,1367,1522

%N Numbers k such that semiprime(semiprime(k)) + 1 = semiprime(semiprime(k+1)).

%C Numbers k such that A001358(A001358(k)) + 1 = A001358(A001358(k+1)).

%C Numbers k such that A091022(k) + 1 = A091022(k+1).

%e 3 is a term because semiprime(semiprime(3)) + 1 = 25 + 1 = semiprime(semiprime(3+1)).

%p A091022 := proc(n) A001358(A001358(n)) ; end proc: isA176658 := proc(n) A091022(n)+1 = A091022(n+1) ; end proc: for n from 1 to 1600 do if isA176658(n) then printf("%d,",n) ; end if; end do: # _R. J. Mathar_, Apr 26 2010

%Y Cf. A001358, A091022.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Apr 23 2010

%E Corrected (72 inserted, 85 replaced by 95, 124 inserted) and extended by _R. J. Mathar_, Apr 26 2010

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Last modified August 12 23:19 EDT 2020. Contains 336440 sequences. (Running on oeis4.)