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A368383
a(n) = index of n in A368382, or -1 if n is missing from that sequence.
1
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
1,2
PROG
(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
CROSSREFS
Sequence in context: A006577 A337150 A280234 * A073652 A277848 A248285
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Mar 03 2024
STATUS
approved