The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 (list; graph; refs; listen; history; text; internal format)
 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 k-gonal 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*(n-2) + 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 14 15:18 EDT 2021. Contains 342949 sequences. (Running on oeis4.)