A358861 a(n) is the smallest centered n-gonal number divisible by exactly n centered n-gonal numbers.

64, 925, 2976, 93457, 866272, 11025, 3036880, 18412718645101, 9283470627432, 201580440699781, 92839099743040, 5236660451226975, 66779973961058176

Offset

3,1

Comments

a(17) = 1415913990579036. - Daniel Suteu, Dec 10 2022

Links

Table of n, a(n) for n=3..15.

Eric Weisstein's World of Mathematics, Centered Polygonal Number

Index entries for sequences related to divisors of numbers

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

Cf. A005179, A358541, A358859, A358860.

Sequence in context: A185368 A027003 A265620 * A253133 A302321 A303015

Adjacent sequences: A358858 A358859 A358860 * A358862 A358863 A358864

Keyword

nonn,more

Author

Ilya Gutkovskiy, Dec 03 2022

Extensions

a(10)-a(15) from Daniel Suteu, Dec 06 2022

Status

approved