A251393 Indices of powers of 2 in A098550.

1, 2, 4, 6, 14, 29, 65, 137, 277, 546, 1109, 2208, 4391, 8746, 17404, 34662, 69036, 137604, 274385, 547278, 1091962, 2179171

Offset

1,2

Links

Table of n, a(n) for n=1..22.

Rémy Sigrist, C program

Formula

A209229(A098550(a(n))) = 1;

A098550(a(n)) = 2^(n-1).

Prog

(Haskell)
a251393 n = a251393_list !! (n-1)
a251393_list = filter ((== 1) . a209229 . a098550) [1..]
(Python)
from fractions import gcd
A251393_list, l1, l2, s, p2, b = [1, 2], 3, 2, 4, 4, {}
for n in range(4, 10**4):
....i = s
....while True:
........if not i in b and gcd(i, l1) == 1 and gcd(i, l2) > 1:
............l2, l1, b[i] = l1, i, 1
............while s in b:
................b.pop(s)
................s += 1
............if i == p2:
................A251393_list.append(n)
................p2 *= 2
............break
........i += 1 # Chai Wah Wu, Dec 03 2014
(C) See Links section.

Crossrefs

Cf. A098550, A000961, A209229, A251394, subsequence of A251241.

Sequence in context: A251581 A151794 A181528 * A058059 A053686 A080198

Adjacent sequences: A251390 A251391 A251392 * A251394 A251395 A251396

Keyword

nonn,more

Author

Reinhard Zumkeller, Dec 03 2014

Extensions

a(18)-a(19) from Chai Wah Wu, Dec 03 2014

a(20) from Chai Wah Wu, Dec 04 2014

a(21)-a(22) from Rémy Sigrist, Nov 08 2022

Status

approved