|
|
A030664
|
|
Product of largest prime <= n and smallest prime >= n.
|
|
6
|
|
|
1, 1, 4, 9, 15, 25, 35, 49, 77, 77, 77, 121, 143, 169, 221, 221, 221, 289, 323, 361, 437, 437, 437, 529, 667, 667, 667, 667, 667, 841, 899, 961, 1147, 1147, 1147, 1147, 1147, 1369, 1517, 1517, 1517, 1681, 1763, 1849, 2021, 2021, 2021, 2209, 2491, 2491, 2491
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
COMMENTS
|
Symmetrical about zero, a(n)=a(-n) if n>1, if negative primes are recognized. - Robert G. Wilson v, Feb 28 2011
Iff n is a prime then a(n)=n^2, otherwise a(n) is a semiprime. - Robert G. Wilson v, Feb 28 2011
|
|
LINKS
|
|
|
FORMULA
|
|
|
MATHEMATICA
|
f[n_] := If[Abs[n] < 2, 1, NextPrime[n + 1, -1] NextPrime[n - 1]]; Array[f, 51, 0] (* Robert G. Wilson v, Feb 28 2011 *)
|
|
PROG
|
(MuPAD) numlib::prevprime(i)*nextprime(i) $ i = 0..50 // Zerinvary Lajos, Feb 26 2007
(Haskell)
(PARI) a(n) = if (n < 2, 1, precprime(n)*nextprime(n)); \\ Michel Marcus, Mar 21 2015
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,nonn,nice
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|