OFFSET
1,2
COMMENTS
Numbers k such that 2^t*3^u + 1 = prime(k).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..166
EXAMPLE
a(1) = 1 because 2^0 * 3^0 + 1 = 2 = prime(1).
a(2) = 2 because 2^1 * 3^0 + 1 = 3 = prime(2).
MATHEMATICA
With[{lim = 10^7}, PrimePi[Select[Sort@ Flatten@ Table[2^i * 3^j + 1, {i, 0, Log2[lim]}, {j, 0, Log[3, lim/2^i]}], PrimeQ]]] (* Amiram Eldar, Sep 02 2024 *)
PROG
(PARI) lista(lim) = {my(s = List()); for(i = 0, logint(lim, 2), for(j = 0, logint(lim >> i, 3), listput(s, 2^i * 3^j + 1))); s = Set(s); for(i = 1, #s, if(isprime(s[i]), print1(primepi(s[i]), ", "))); } \\ Amiram Eldar, Sep 02 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Mar 07 2010
EXTENSIONS
Corrected and extended by Charles R Greathouse IV, Mar 21 2010
STATUS
approved