A048205 a(n)=T(n+2,n), array T given by A048201.

4, 9, 17, 27, 41, 56, 72, 93, 115, 140, 166, 194, 227, 261, 296, 332, 370, 410, 452, 498, 546, 595, 645, 698, 755, 815, 877, 941, 1006, 1076, 1153, 1233, 1314, 1397, 1482, 1568, 1658, 1749, 1841, 1941, 2045, 2152, 2260, 2376

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• changed

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A004978.

Programs

Python

from itertools import count, accumulate, islice
from collections import deque
def A048205_gen(): # generator of terms
    aset, alist, c = {1,3}, deque([2,1]), 0
    for k in count(3):
        if k in aset:
            aset.remove(k)
        else:
            yield (c:=c+k)
            aset |= set(k+d for d in accumulate(alist))
            alist.appendleft(k)
A048205_list = list(islice(A048205_gen(),50)) # Chai Wah Wu, Sep 02 2025

Formula

a(n) = A004978(n+3) - 4. - Sean A. Irvine, Jun 05 2021