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a(n) = index of n in A368382, or -1 if n is missing from that sequence.
1

%I #25 Apr 20 2024 03:01:12

%S 1,7,2,5,13,3,67,35,11,33,4,31,6,29,8,27,63,25,327,23,61,21,325,19,59,

%T 17,323,15,57,9,321,175,55,173,15490,171,53,169,317,167,51,165,1167,

%U 163,49,161,10,159,47,157,12,155,45,153,14,151,16,149,18,147,20,145,22,143,24,141,26,139,28,137,30,135,32,133,34

%N a(n) = index of n in A368382, or -1 if n is missing from that sequence.

%H Chai Wah Wu, <a href="/A368383/b368383.txt">Table of n, a(n) for n = 1..10000</a>

%o (Python)

%o from itertools import count

%o def A368383(n):

%o a, aset, p = 1, {0,1}, 2

%o for c in count(1):

%o if a==n: return c

%o for b in count(a%p,p):

%o if b not in aset:

%o aset.add(b)

%o a, p = b, 3 if p == 2 else p+2

%o break # _Chai Wah Wu_, Mar 05 2024

%o (Python) # faster for initial segment of sequence

%o def A368383_gen(): # uses A368382_gen/imports from _Chai Wah Wu_ in A368382

%o adict, n = dict(), 1

%o for i, v in enumerate(A368382_gen(), 1):

%o if v >= n and v not in adict:

%o adict[v] = i

%o while n in adict:

%o yield adict[n]; del adict[n]; n += 1

%o print(list(islice(A368383_gen(), 63))) # _Michael S. Branicky_, Apr 18 2024

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Mar 03 2024