A352928 The smallest unused number when A093714(n) is being calculated.

1, 2, 2, 4, 4, 6, 6, 8, 8, 9, 9, 10, 10, 10, 12, 12, 15, 15, 16, 16, 16, 18, 18, 20, 20, 24, 24, 24, 24, 28, 28, 28, 28, 30, 30, 30, 30, 34, 34, 36, 36, 36, 36, 40, 40, 42, 42, 42, 42, 42, 42, 48, 48, 50, 50, 54, 54, 54, 54, 58, 58, 60, 60, 60, 60, 64, 64, 66, 66, 66, 66, 70, 70

Offset

1,2

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Mathematica

nn = 120; c[_] = 0; a[1] = c[1] = 1; u = 2; {1}~Join~Reap[Do[k = u; While[Nand[c[k] == 0, CoprimeQ[#, k], k != # + 1], k++] &@ a[i - 1]; Set[{a[i], c[k]}, {k, i}]; If[a[i] == u, While[c[u] > 0, u++]], {i, 2, nn}]][[-1, -1]] (* Michael De Vlieger, May 02 2022 *)

Prog

(Python)
from math import gcd
from itertools import islice
def agen(): # generator of terms
    an, aset, mink = 1, {1}, 2
    yield 1
    while True:
        yield mink
        k = mink
        while k in aset or gcd(an, k) != 1 or k-an == 1: k += 1
        an = k
        aset.add(an)
        while mink in aset: mink += 1
print(list(islice(agen(), 72))) # Michael S. Branicky, May 02 2022

Crossrefs

Cf. A093714.

Sequence in context: A116568 A239933 A061106 * A319399 A352434 A161764

Adjacent sequences: A352925 A352926 A352927 * A352929 A352930 A352931

Keyword

nonn

Author

N. J. A. Sloane, May 02 2022

Status

approved