OFFSET
1,2
COMMENTS
C(n) gives the maximum number of pieces in which a circular disc can be cut with n slices (A000124). C. Pickover calls the C(n)s "cake integers".
REFERENCES
Pickover, C. "Wonders of Numbers", Oxford Univ. Press, 2001; page 158, ch. 65.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review
FORMULA
a(n) = (A110872(n) - 1)/2. - Ray Chandler, Oct 08 2005
EXAMPLE
C(7) = (7^2 + 7 + 2)/2 = 29, a prime, so 7 is a term of the sequence.
MATHEMATICA
Select[ Range[300], PrimeQ[(#^2 + # + 2)/ 2] &]
PROG
(Magma) [n: n in [1..300] | IsPrime((n^2 + n + 2) div 2)]; // Vincenzo Librandi, Sep 30 2012
(PARI) is(n)=isprime(n*(n+1)/2+1) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Joseph L. Pe, Feb 19 2002
EXTENSIONS
Edited by Robert G. Wilson v, Feb 19 2002
STATUS
approved