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A036098 Centered cube numbers: a(n) = (n+1)^20 + n^20. 3
1, 1048577, 3487832977, 1102998412177, 96466943268401, 3751525871703601, 83448424737674977, 1232713770904458977, 13310586963663775777, 112157665459056928801, 772749994932560009201, 4506509987380035131377 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
Never prime because a(n) = (2n^4 + 4n^3 + 6n^2 + 4n + 1) * (n^16 + 8n^15 + 76n^14 + 392n^13 + 1394n^12 + 3632n^11 + 7112n^10 + 10656n^9 + 12376n^8 + 11220n^7 + 7942n^6 + 4356n^5 + 1819n^4 + 560n^3 + 120n^2 + 16n + 1). Semiprime for n in {1, 13, 14, 54, 162, ...}. - Jonathan Vos Post, Aug 27 2011
LINKS
B. K. Teo and N. J. A. Sloane, Magic numbers in polygonal and polyhedral clusters, Inorgan. Chem. 24 (1985), 4545-4558.
EXAMPLE
a(1) = 1^20 + (1+1)^20 = 1048577 = 17 * 61681, which is semiprime.
PROG
(Magma) [(n+1)^20+n^20: n in [0..20]]; // Vincenzo Librandi, Aug 28 2011
CROSSREFS
Sequence in context: A351316 A017703 A013968 * A203668 A253312 A253660
KEYWORD
nonn,easy
AUTHOR
STATUS
approved

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Last modified May 27 15:55 EDT 2024. Contains 372880 sequences. (Running on oeis4.)