A368383 a(n) = index of n in A368382, or -1 if n is missing from that sequence.

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

Offset: 1

Author

N. J. A. Sloane, Mar 03 2024

Keywords

• nonn

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..10000

Programs

Python

from itertools import count
def A368383(n):
    a, aset, p = 1, {0,1}, 2
    for c in count(1):
        if a==n: return c
        for b in count(a%p,p):
            if b not in aset:
                aset.add(b)
                a, p = b, 3 if p == 2 else p+2
                break # Chai Wah Wu, Mar 05 2024

Python

# faster for initial segment of sequence
def A368383_gen(): # uses A368382_gen/imports from Chai Wah Wu in A368382
    adict, n = dict(), 1
    for i, v in enumerate(A368382_gen(), 1):
        if v >= n and v not in adict:
            adict[v] = i
            while n in adict:
                yield adict[n]; del adict[n]; n += 1
print(list(islice(A368383_gen(), 63))) # Michael S. Branicky, Apr 18 2024