A358417 Indices of the triangular numbers in A189475.

1, 2, 6, 18, 54, 29, 182, 546, 1638, 4914, 1407, 1599, 726, 581, 945, 16362, 1536, 49278, 2175, 7077, 22238, 4224, 6266, 10632, 21440, 38454, 21189, 12801, 219138, 47039, 37494, 119837, 19158, 760898, 182840, 7649, 536847, 75405, 544775, 160520, 365439, 307943

Offset

1,2

Links

Table of n, a(n) for n=1..42.

Formula

A000217(a(n)) = A189475(n).

Prog

(Python)
from itertools import islice, count
from sympy import integer_nthroot
def A358417_gen(): # generator of terms
    a = 0
    for n in count(1):
        c, d = integer_nthroot(((b:=n**2)-a<<3)+1, 2)
        if d:
            yield c-1>>1
            a = b
A358417_list = list(islice(A358417_gen(), 44))

Crossrefs

Cf. A000217, A036449, A189475, A358416.

Sequence in context: A094864 A120010 A132790 * A372899 A214799 A072850

Adjacent sequences: A358414 A358415 A358416 * A358418 A358419 A358420

Keyword

nonn

Author

Chai Wah Wu, Nov 14 2022

Status

approved