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A263457 Integers m such that A006218(m) is triangular. 1
1, 2, 5, 15, 20, 26, 55, 68, 92, 108, 150, 156, 336, 346, 364, 423, 563, 586, 682, 798, 866, 951, 1194, 1734, 1888, 2790, 3102, 3150, 3506, 4210, 4611, 5820, 6766, 6943, 7665, 7701, 7888, 8734, 8772, 9410, 10114, 10839, 10969, 11014, 11453, 11630, 11947, 12357 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
EXAMPLE
If A027750 is displayed as a regular triangle:
1; <--1
1, 2; <--2
1, 3; 1,
2, 4; 1, 5; <--5
1, 2, 3, 6; 1,
7; 1, 2, 4, 8; 1,
3, 9; 1, 2, 5, 10; 1,
11; 1, 2, 3, 4, 6, 12; 1,
13; 1, 2, 7, 14; 1, 3, 5, 15; <-- 15
PROG
(PARI) lista(nn) = {s = 0; for (n=1, nn, s += numdiv(n); if (ispolygonal(s, 3), print1(n, ", ")); ); }
(Python)
from sympy import integer_nthroot, divisor_count
A263457_list, s = [], 0
for n in range(1, 10**4):
s += divisor_count(n)
if integer_nthroot(8*s+1, 2)[1]:
A263457_list.append(n) # Chai Wah Wu, Oct 09 2021
CROSSREFS
Sequence in context: A058221 A349734 A146122 * A146121 A066883 A146120
KEYWORD
nonn
AUTHOR
Michel Marcus, Oct 19 2015
STATUS
approved

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Last modified June 20 10:31 EDT 2024. Contains 373516 sequences. (Running on oeis4.)