This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
In range [2^(6-1),(2^6)-1] ([32,63]) of permutations A209861 & A209862, there are 6 cycles of size 1 (fixed points), 2 cycles of size 3, one cycle of size 4, and 2 cycles of size 8 (6 + 2*3 + 4 + 2*8 = 32), thus a(6) = lcm(1,3,4,8) = 24.
In range [2^(6-1),(2^6)-1] ([32,63]) of permutations A209861 & A209862, there are 6 cycles of size 1 (six fixed points), 2 cycles of size 3, one cycle of size 4, and 2 cycles of size 8, 6*1 + 2*3 + 1*4 + 2*8 = 32 in total, of which 6*1 + 2*3 elements are in odd-sized cycles, thus a(6)=12.
In range [2^(6-1),(2^6)-1] ([32,63]) of permutations A209861 & A209862, there are 6 cycles of size 1 (six fixed points), 2 cycles of size 3, one cycle of size 4, and 2 cycles of size 8, i.e. 6*1 + 2*3 + 1*4 + 2*8 = 32 in total, of which 4 + 2*8 elements are in even-sized cycles, thus a(6)=20.
From _Gus Wiseman_, Aug 24 2021: (Start)
The terms, their binary expansions, and their binary indices begin:
0: ~ {}
1: 1 ~ {1}
2: 10 ~ {2}
3: 11 ~ {1,2}
4: 100 ~ {3}
5: 101 ~ {1,3}
6: 110 ~ {2,3}
7: 111 ~ {1,2,3}
8: 1000 ~ {4}
9: 1001 ~ {1,4}
10: 1010 ~ {2,4}
12: 1100 ~ {3,4}
11: 1011 ~ {1,2,4}
13: 1101 ~ {1,3,4}
14: 1110 ~ {2,3,4}
15: 1111 ~ {1,2,3,4}
(End)
a(12)=3, as 12 occurs as the 3rd term (zero-based) in A209641. a(14)=0, as 14 doesn't occur in A209641.
(define (A209640 n) (if (or (zero? n) (not (member_of_A209641? n))) 0 (let* ((w (/ (binwidth n) 2))) (let loop ((rank 0) (row 1) (u (- w 1)) (n (- n (A053644 n))) (i (/ (A053644 n) 2)) (first_0_found? #f)) (cond ((or (zero? row) (zero? u) (zero? n)) (+ (expt 2 (-1+ w)) rank)) ((> i n) (loop rank (- row 1) u n (/ i 2) #t)) (else (loop (+ rank (if first_0_found? (A007318tr (- (+ row u) 1) (- row 1)) (A007318tr (- w 1) (- row 1)))) (+ row 1) (- u 1) (- n i) (/ i 2) first_0_found?))))))) (define (binwidth n) (let loop ((n n) (i 0)) (if (zero? n) i (loop (floor->exact (/ n 2)) (1+ i)))))
def a(n):
s=0
i=1
while n!=0:
if n%2==0:
n//=2
s=4*s + 1
else:
n=(n - 1)//2
s=(s + i)*2
i*=4
return s
print([a(n) for n in range(101)]) # Indranil Ghosh, May 25 2017, translated from Antti Karttunen's SCHEME code
(define (A209642 n) (let loop ((n n) (s 0) (i 1)) (cond ((zero? n) s) ((even? n) (loop (/ n 2) (+ (* 4 s) 1) (* i 4))) (else (loop (/ (- n 1) 2) (* 2 (+ s i)) (* i 4))))))
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