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 A089733 Begin with 1; add a distinct prime to get a composite number, then add a distinct composite number to get a prime; repeat. 0

%I

%S 1,4,13,15,19,24,59,66,131,142,157,170,191,208,233,252,307,330,379,

%T 408,499,530,557,594,709,750,827,870,991,1038,1123,1176,1301,1360,

%U 1399,1460,1493,1560,1693,1764,1907,1980,2099,2178,2273,2356,2437,2526,2671,2768

%N Begin with 1; add a distinct prime to get a composite number, then add a distinct composite number to get a prime; repeat.

%C a(2n) - a(2n-1) = prime(n) for n > 2.

%p p:=[]:c:=[]:a:=[1]:for n from 2 to 60 do for i from 2 do m:=a[n-1]+i: if n mod 2=0 then if isprime(i) and not isprime(m) and not member(i,p) then p:=[op(p),i]: a:=[op(a),m]: break fi else if isprime(m) and not isprime(i) and not member(i,c) then c:=[op(c),i]: a:=[op(a),m]: break fi fi od od: op(a); # C. Ronaldo

%K base,nonn

%O 1,2

%A _Amarnath Murthy_, Nov 19 2003

%E More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 26 2004

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Last modified April 1 14:50 EDT 2023. Contains 361695 sequences. (Running on oeis4.)