A365301 a(n) is the smallest nonnegative integer such that the sum of any five ordered terms a(k), k<=n (repetitions allowed), is unique.

0, 1, 6, 31, 108, 366, 926, 2286, 5733, 12905, 27316, 44676, 94545, 147031, 257637, 435387, 643320, 1107715, 1760092, 2563547, 3744446, 5582657, 8089160, 11373419, 15575157, 21480927, 28569028, 40893371, 53425354, 69774260, 93548428, 119627554

Offset

1,3

Comments

This is the greedy B_5 sequence.

Links

Table of n, a(n) for n=1..32.

J. Cilleruelo and J Jimenez-Urroz, B_h[g] sequences, Mathematika (47) 2000, pp. 109-115.

Melvyn B. Nathanson, The third positive element in the greedy B_h-set, arXiv:2310.14426 [math.NT], 2023.

Melvyn B. Nathanson and Kevin O'Bryant, The fourth positive element in the greedy B_h-set, arXiv:2311.14021 [math.NT], 2023.

Kevin O'Bryant, A complete annotated bibliography of work related to Sidon sequences, Electron. J. Combin., DS11, Dynamic Surveys (2004), 39 pp.

Example

a(4) != 20 because 20+1+1+1+1 = 6+6+6+6+0.

Prog

(Python)
def GreedyBh(h, seed, stopat):
    A = [set() for _ in range(h+1)]
    A[1] = set(seed)    # A[i] will hold the i-fold sumset
    for j in range(2, h+1): # {2, ..., h}
        for x in A[1]:
            A[j].update([x+y for y in A[j-1]])
    w = max(A[1])+1
    while w <= stopat:
        wgood = True
        for k in range(1, h):
            if wgood:
                for j in range(k+1, h+1):
                    if wgood and (A[j].intersection([(j-k)*w + x for x in A[k]]) != set()):
                        wgood = False
        if wgood:
            A[1].add(w)
            for k in range(2, h+1): # update A[k]
                for j in range(1, k):
                    A[k].update([(k-j)*w + x for x in A[j]])
        w += 1
        return A[1]
GreedyBh(5, [0], 10000)
(Python)
from itertools import count, islice, combinations_with_replacement
def A365301_gen(): # generator of terms
    aset, alist = set(), []
    for k in count(0):
        bset = set()
        for d in combinations_with_replacement(alist+[k], 4):
            if (m:=sum(d)+k) in aset:
                break
            bset.add(m)
        else:
            yield k
            alist.append(k)
            aset |= bset
A365301_list = list(islice(A365301_gen(), 10)) # Chai Wah Wu, Sep 01 2023

Crossrefs

Row 5 of A365515.

Cf. A025582, A051912, A365300, A365302, A365303, A365304, A365305.

Sequence in context: A143568 A351935 A356608 * A337574 A166786 A003728

Adjacent sequences: A365298 A365299 A365300 * A365302 A365303 A365304

Keyword

nonn,more

Author

Kevin O'Bryant, Aug 31 2023

Extensions

a(18)-a(28) from Chai Wah Wu, Sep 01 2023

a(29)-a(30) from Chai Wah Wu, Sep 10 2023

a(31)-a(32) from Chai Wah Wu, Mar 02 2024

Status

approved