

A177029


Numbers that have exactly two different representations as polygonal numbers.


11



6, 9, 10, 12, 16, 18, 22, 24, 25, 27, 30, 33, 34, 35, 39, 40, 42, 46, 48, 49, 52, 54, 57, 58, 60, 63, 65, 69, 72, 76, 82, 84, 85, 87, 88, 90, 92, 93, 94, 95, 99, 102, 106, 108, 114, 115, 118, 121, 123, 124, 125, 129, 130, 132, 133, 138, 142, 147, 150, 155, 159, 160, 162, 166, 168
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OFFSET

1,1


COMMENTS

Numbers that have only A177025(.)=1 representation are listed by A090467.


LINKS

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


FORMULA

{m: A177025(m)=2}.


EXAMPLE

6 is a triangular and a hexagonal number, but is not any other kgonal number.


PROG

(PARI) lista(nn) = {for (n=1, nn, if (sum(k=3, n, ispolygonal(n, k)) == 2, print1(n, ", ")); ); } \\ Michel Marcus, Mar 25 2015
(Python)
A177029_list = []
for m in range(1, 10**4):
n, c = 3, 0
while n*(n+1) <= 2*m:
if not 2*(n*(n2) + m) % (n*(n  1)):
c += 1
if c > 1:
break
n += 1
if c == 1:
A177029_list.append(m) # Chai Wah Wu, Jul 28 2016


CROSSREFS

Cf. A177025, A090467, A177028, A000217, A000326, A000384, A000566, A000567, A176949, A176948, A176774, A176744, A176747, A176775, A175873, A176874.
Sequence in context: A039725 A262362 A125494 * A105066 A048283 A169692
Adjacent sequences: A177026 A177027 A177028 * A177030 A177031 A177032


KEYWORD

nonn


AUTHOR

Vladimir Shevelev, May 01 2010


EXTENSIONS

Extended by R. J. Mathar, Aug 15 2010


STATUS

approved



