OFFSET
0,2
COMMENTS
Can never be prime, as a(n) = (2n + 1) * (n^22 + 11n^21 + 121n^20 + 825n^19 + 4015n^18 + 14817n^17 + 43065n^16 + 101046n^15 + 194634n^14 + 311278n^13 + 416394n^12 + 467842n^11 + 442118n^10 + 350974n^9 + 233108n^8 + 128603n^7 + 58277n^6 + 21335n^5 + 6157n^4 + 1349n^3 + 211n^2 + 21n + 1). a(1) is semiprime (A001358). [Jonathan Vos Post, Aug 28 2011]
REFERENCES
B. K. Teo and N. J. A. Sloane, Magic numbers in polygonal and polyhedral clusters, Inorgan. Chem. 24 (1985), 4545-4558.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..10000
EXAMPLE
a(2) = 1^23 + (1+1)^23 = 8388609 = 3 * 2796203, which is semiprime.
MATHEMATICA
Total/@Partition[Range[0, 20]^23, 2, 1] (* Harvey P. Dale, Nov 02 2023 *)
PROG
(Magma) [(n+1)^23+n^23: n in [0..20]]; // Vincenzo Librandi, Aug 28 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved