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a(n) is the difference between F=A000045(n) and the largest prime not exceeding F.
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%I #19 Aug 29 2024 13:55:49

%S 0,0,0,1,0,2,3,2,0,5,0,4,3,4,0,5,4,2,7,4,0,17,8,14,31,14,0,37,20,26,9,

%T 20,22,11,6,12,15,32,18,17,0,16,43,24,0,17,20,26,27,20,6,9,12,34,29,

%U 36,30,47,48,4,45,32,54,27,132,22,31,4,32,11,12,60,7,76

%N a(n) is the difference between F=A000045(n) and the largest prime not exceeding F.

%H Amiram Eldar, <a href="/A375751/b375751.txt">Table of n, a(n) for n = 3..10000</a>

%F a(n) = A000045(n) - A138184(n).

%F a(n) = 0 <=> n in { A001605 }. - _Alois P. Heinz_, Aug 27 2024

%p a:= n-> (F-> F-prevprime(F+1))(combinat[fibonacci](n)):

%p seq(a(n), n=3..76); # _Alois P. Heinz_, Aug 27 2024

%t a[n_]:=Module[{p=2},While[(f=Fibonacci[n])>=p, pold=p;p=NextPrime[p]]; d=f-pold;If[d>0,f-pold,d=0]; d]; Array[a,74,3] (* _Stefano Spezia_, Aug 27 2024 *)

%t Map[(# - NextPrime[# + 1, -1]) &, Fibonacci[Range[3, 76]]] (* _Amiram Eldar_, Aug 29 2024 *)

%o (PARI) a(n) = my(F=fibonacci(n)); F-precprime(F)

%o (Python)

%o from sympy import prevprime, fibonacci

%o def A375753(n): return (F:=fibonacci(n)) - prevprime(F+1) # _Karl-Heinz Hofmann_, Aug 27 2024

%Y Cf. A000045, A007917, A001605, A138184, A138185, A159977, A159978, A202090.

%K nonn,easy

%O 3,6

%A _Hugo Pfoertner_, Aug 27 2024