A376201 Fixed points in A376198.

1, 2, 3, 4, 11, 12, 27, 28, 59, 60, 123, 124, 125, 126, 255, 256, 515, 516, 517, 518, 519, 520, 1043, 1044, 1045, 1046, 1047, 1048, 2099, 2100, 2101, 2102, 2103, 2104, 2105, 2106, 2107, 2108, 2109, 2110, 4223, 4224, 4225, 4226, 4227, 4228, 8459, 8460, 16923, 16924, 16925, 16926, 33855, 33856, 67715, 67716, 67717, 67718, 67719

Offset: 1

Author

N. J. A. Sloane, Oct 03 2024

Keywords

• nonn

Comments

Conjectures: the terms consist of runs of an even number (>1) of successive numbers that increase by 1 at each step; A376758(n) is one-half of the length of the n-th such run; and the run ends at A376751(n) - 1. - N. J. A. Sloane, Oct 07 2024

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..398

Crossrefs

Cf. A376198-A376200, A376750-A376754, A376758.

Programs

Python

from itertools import count, islice
from sympy import isprime, nextprime
def agen(): # generator of terms
    an, smc, smp = 2, 4, 3
    yield from [1, 2]
    for n in count(3):
        if not isprime(an):
            an = smp if an == 2*smp else smc
        else:
            an = smp if smp < smc else smc
        if an == smp: smp = nextprime(smp)
        else:
            smc += 1
            while isprime(smc): smc += 1
        if n == an: yield an
print(list(islice(agen(), 59))) # Michael S. Branicky, Oct 03 2024