A376584 Fixed points in A375564.

1, 2, 3, 4, 15, 51, 63, 363, 437, 729, 1385, 1388, 1413, 2807, 5418, 5422, 5428, 5435, 5451, 5537, 10790, 10795, 10803, 10871, 21505, 21507, 21899, 22081, 42969, 43073, 43387, 44069, 171631, 172889, 342493, 2747813, 5464783, 10908941, 10911583, 87259373, 87327187, 174579089

Offset: 1

Author

Scott R. Shannon, Sep 29 2024

Keywords

• nonn

Crossrefs

Cf. A375564, A376189, A376191, A376192, A376193, A376195.

Programs

Python

from itertools import count, islice
from math import gcd
from sympy import isprime
def A376584_gen(): # generator of terms
    aset, a, b = {1,2}, 2, 3
    yield from (1,2)
    for i in count(3):
        c = b
        if isprime(a):
            while c in aset or gcd(c,a)>1:
                c+=1
        else:
            while c in aset or gcd(c,a)==1:
                c+=1
        aset.add(a:=c)
        if i == c:
            yield i
        while b in aset:
            b += 1
A376584_list = list(islice(A376584_gen(),20)) # Chai Wah Wu, Sep 30 2024

Extensions

a(40)-a(42) from Scott R. Shannon, Oct 02 2024