A350278 Index of first occurrence of n in A349325.

1, 3, 6, 7, 14, 19, 54, 109, 110, 73, 146, 145, 328, 129, 342, 345, 398, 337, 462, 313, 3708, 353, 470, 14673, 5838, 10855, 23718, 14473, 60216, 26283, 60220, 60221, 500726, 155897, 1098404, 445089, 1098406, 1316099, 1168014, 1386505, 3932646, 1169865, 4424230

Offset

1,2

Links

Chai Wah Wu, Table of n, a(n) for n = 1..82

Index entries for sequences related to 3x+1 (or Collatz) problem

Example

a(5) = 14 because 5 occurs for the first time at position 14 in A349325.

Mathematica

A349325[n_]:=A349325[n]=Module[{h=1, c=n, prevc=n}, While[c>1, If[OddQ[c], c=(3c+1)/2; If[prevc<n&&c>n, h++], c/=2^IntegerExponent[c, 2]; If[prevc>n&&c<n, h++]]; prevc=c]; h]
nterms=30; Table[i=0; While[A349325[++i]!=n]; i, {n, nterms}]

Prog

(Python)
def A349325(n):
    prevc = c = n
    h = 1
    while c > 1:
        if c % 2:
            c = (3*c+1) // 2
            if prevc < n and c > n: h += 1
        else:
            c //= 2
            if prevc > n and c < n: h += 1
        prevc = c
    return h
def A349325_fo_idx(n):
    i = 1
    while A349325(i) != n:
        i += 1
    return i
print([A349325_fo_idx(n) for n in range(1, 20)])

Crossrefs

Cf. A349325, A350277.

Sequence in context: A359476 A070523 A350277 * A233757 A341622 A139247

Adjacent sequences: A350275 A350276 A350277 * A350279 A350280 A350281

Keyword

nonn,hard

Author

Paolo Xausa, Dec 22 2021

Extensions

a(36)-a(43) from Chai Wah Wu, Jan 04 2022

Status

approved