OFFSET
0,2
COMMENTS
After a(0) always has at least 4 prime factors, because a(n) = (2n + 1) * (n^2 + n + 1) * (n^6 + 3n^5 + 9n^4 + 13n^3 + 11n^2 + 5n + 1) * (n^12 + 6n^11 + 63n^10 + 260n^9 + 643n^8 + 1078n^7 + 1275n^6 + 1078n^5 + 650n^4 + 274n^3 + 77n^2 + 13n + 1). [Jonathan Vos Post, Aug 27 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
MATHEMATICA
Total/@Partition[Range[0, 20]^21, 2, 1] (* Harvey P. Dale, Jul 02 2019 *)
PROG
(Magma) [(n+1)^21+n^21: n in [0..20]]; // Vincenzo Librandi, Aug 28 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved