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A126286 a(1) = 2, a(n) = n * LeastPrimeFactor(n+1) / LeastPrimeFactor(n). 5
2, 3, 2, 10, 2, 21, 2, 12, 6, 55, 2, 78, 2, 21, 10, 136, 2, 171, 2, 30, 14, 253, 2, 60, 10, 39, 18, 406, 2, 465, 2, 48, 22, 85, 14, 666, 2, 57, 26, 820, 2, 903, 2, 66, 30, 1081, 2, 168, 14, 75, 34, 1378, 2, 135, 22, 84, 38, 1711, 2, 1830, 2, 93, 42, 160, 26, 2211, 2, 102, 46 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = A032742(n)*A020639(n+1), for n>1. - Ivan Neretin, May 20 2015
EXAMPLE
a(6) = (6 / LeastPrimeFactor(6)) * LeastPrimeFactor(7) = 21.
MATHEMATICA
a[1] := 2; a[n_] := n*FactorInteger[n + 1][[1, 1]]/FactorInteger[n][[1, 1]]; Table[a[n], {n, 69}] (* Ivan Neretin, May 20 2015 *)
PROG
(PARI) a(n) = if (n==1, 2, n*factor(n+1)[1, 1]/factor(n)[1, 1]); \\ Michel Marcus, Aug 14 2013
CROSSREFS
Sequence in context: A336246 A351251 A362988 * A126288 A205393 A075076
KEYWORD
easy,nonn
AUTHOR
Lior Manor, Dec 25 2006
STATUS
approved

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)