OFFSET
0,2
COMMENTS
All terms are odd and equal to p - 2 for some prime p. Definition assumes that a(i+1) > a(i) as otherwise adding 1 to any initial subsequence would still satisfy the definition. - Chai Wah Wu, Jan 12 2019
For n >= 2, the last digit of a(n) is 5 or 9. - Pontus von Brömssen, Oct 12 2023
EXAMPLE
1*3 + 2, 3*5 + 2, 1*5 + 2, etc. are primes.
9*1 + 2 = 11, 9*3 + 2 = 29, 9*5 + 2 = 47 are all primes, therefore a(4) = 9.
MATHEMATICA
a = {1}; For[n = 2, n < 1000000, n++, b = Table[a[[i]]*n + 2, {i, 1, Length[ a]}]; If[Union[PrimeQ[b], PrimeQ[b]] == {True}, AppendTo[a, n]]]; a (* Stefan Steinerberger, Jun 02 2007 *)
CROSSREFS
Cf. A083518.
KEYWORD
hard,more,nonn
AUTHOR
Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 05 2003
EXTENSIONS
Corrected and extended by Stefan Steinerberger, Jun 02 2007
a(10) from Donovan Johnson, Nov 11 2008
STATUS
approved