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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 Chai Wah Wu, Table of n, a(n) for n = 1..1000 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 Cf. A000005, A006218, A027750, A175345. Sequence in context: A058221 A349734 A146122 * A146121 A066883 A146120 Adjacent sequences: A263454 A263455 A263456 * A263458 A263459 A263460 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.)