|
|
A358861
|
|
a(n) is the smallest centered n-gonal number divisible by exactly n centered n-gonal numbers.
|
|
4
|
|
|
64, 925, 2976, 93457, 866272, 11025, 3036880, 18412718645101, 9283470627432, 201580440699781, 92839099743040, 5236660451226975, 66779973961058176
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
3,1
|
|
COMMENTS
|
|
|
LINKS
|
|
|
EXAMPLE
|
a(5) = 2976, because 2976 is a centered pentagonal number that has 5 centered pentagonal divisors {1, 6, 16, 31, 2976} and this is the smallest such number.
|
|
PROG
|
(PARI) a(n) = if(n<3, return()); for(k=1, oo, my(t=((n*k*(k+1))/2+1)); if(sumdiv(t, d, issquare(8*(d-1)/n + 1) && (sqrtint((8*(d-1))/n + 1)-1)%2 == 0) == n, return(t))); \\ Daniel Suteu, Dec 10 2022
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|