OFFSET
1,1
COMMENTS
Also numbers k such that (2*10^k - 17)/3 is prime.
The terms 1600, 2175, 2978 and 3649 correspond to primes. - Joao da Silva (zxawyh66(AT)yahoo.com), Oct 03 2005
a(37) > 3*10^5, Robert Price, Oct 19 2023
LINKS
FORMULA
a(n) = A056658(n) + 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
EXAMPLE
If n = 4 we get ((2*10^4)-17)/3 = 19983/3 = 6661, which is prime.
MATHEMATICA
Do[ If[ PrimeQ[ 2(10^n - 1)/3 - 5], Print[n]], {n, 0, 7000}]
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Julien Peter Benney (jpbenney(AT)ftml.net), Sep 14 2004
EXTENSIONS
a(21)-a(22) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(23)-a(26) from Kamada link by Ray Chandler, Dec 23 2010
a(27) from Kamada link by Robert Price, Aug 17 2014
a(28)-a(31) from Robert Price, Aug 17 2014
a(32)-a(36) from Robert Price, Oct 19 2023
STATUS
approved