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A342550
For n>=3, a(n) is the sum of the indices of n seen as an m-gonal number.
3
2, 2, 2, 5, 2, 2, 5, 6, 2, 5, 2, 2, 10, 6, 2, 5, 2, 2, 11, 6, 2, 5, 7, 2, 5, 13, 2, 5, 2, 2, 5, 6, 7, 19, 2, 2, 5, 6, 2, 5, 2, 2, 19, 6, 2, 5, 9, 2, 11, 6, 2, 5, 17, 2, 5, 6, 2, 5, 2, 2, 5, 14, 7, 22, 2, 2, 5, 13, 2, 5, 2, 2, 10, 6, 2, 17, 2, 2, 20, 6, 2, 5, 7, 2, 5
OFFSET
3,1
COMMENTS
This sum is constituted of A177025(n) terms related to the n-row of A177028 triangle.
For m in A090467, a(m) = 2.
By definition, a(n) can never be equal to 3 or 4.
Up to 10^7, no n has been found with a(n) = 8, 12 or 18.
LINKS
EXAMPLE
15 is the 5th triangular, the 3rd hexagonal and the 2nd 15-gonal, so a(15) = 5+3+2 = 10.
PROG
(PARI) row(n) = my(v=List()); fordiv(2*n, k, if(k<2, next); if(k==n, break); my(s=(2*n/k-4+2*k)/(k-1)); if(denominator(s)==1, listput(v, s))); Vecrev(v); \\ A177028
a(n) = my(v=row(n), s=0); for (k=1, #v, if ((v[k]>2) && ispolygonal(n, v[k], &i), s += i)); s;
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Mar 27 2021
STATUS
approved