A355238 First occurrence of difference n between two consecutive terms of A000404. a(n) gives the upper term. The lower term is A355237.

18, 10, 5, 17, 25, 80, 97, 145, 386, 3060, 997, 1681, 4194, 6544, 1508, 8450, 9721, 22178, 10728, 5185, 16130, 154730, 58441, 31681, 52418, 401506, 176837, 101377, 105601, 678386, 241913, 501748, 393850, 284036, 685576, 1437389, 1751333, 3225616, 3439297, 2479634

Offset

1,1

Links

Table of n, a(n) for n=1..40.

Formula

a(n) = A355237(n) + n.

Prog

(Python)
from itertools import count
from sympy import factorint
def A355238(n):
    m = 2
    for k in count(2):
        c = False
        for p in (f:=factorint(k)):
            if (q:= p & 3)==3 and f[p]&1:
                break
            elif q == 1:
                c = True
        else:
            if c or f.get(2, 0)&1:
                if k-m == n:
                    return k
                m = k # Chai Wah Wu, Jul 01 2022

Crossrefs

Cf. A000404, A355237.

Sequence in context: A089517 A290345 A035616 * A244093 A195926 A195929

Adjacent sequences: A355235 A355236 A355237 * A355239 A355240 A355241

Keyword

nonn

Author

Hugo Pfoertner, Jun 30 2022

Status

approved