OFFSET
1,2
COMMENTS
Lambda is the function (A002322). If there are infinitely many Sophie Germain primes (conjecture), then this sequence is infinite. Proof: The numbers of the form p(2p+1) are in a subsequence if p and 2p+1 are both prime with p > 3, because from the property that lambda(p(2p+1)) = p(p-1), if m = p(2p+1) then lambda(m+phi(m)) = lambda (p(2p+1) + p(p-1)) = lambda(3p^2) = p(p-1) = lambda(m).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
EXAMPLE
36 is in the sequence because lambda(36) = 6, and lambda(36 + 6) = lambda(42) = 6.
MATHEMATICA
Select[Range[20000], CarmichaelLambda[ #] == CarmichaelLambda[ # + CarmichaelLambda[#] ] &]
PROG
(Magma) [1] cat [n: n in [2..8140] | CarmichaelLambda(n) eq CarmichaelLambda(n+CarmichaelLambda(n))]; // Bruno Berselli, Apr 10 2011
(PARI) lambda(n) = lcm(znstar(n)[2]);
isok(n) = lambda(n) == lambda(n+lambda(n)); \\ Michel Marcus, May 12 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Apr 01 2011
STATUS
approved