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A303090
Numbers k such that 5^k + 2*k is prime.
1
1, 2, 3, 7, 18, 27, 61, 721, 873, 2492, 8713
OFFSET
1,2
COMMENTS
a(12) > 20000. - Jon E. Schoenfield, Apr 19 2018
a(12) > 40000. - Michael S. Branicky, Apr 13 2023
EXAMPLE
1 is a term because 5^1 + 2*1 = 5 + 2 = 7, a prime.
2 is a term because 5^2 + 2*2 = 25 + 4 = 29, a prime.
3 is a term because 5^3 + 2*3 = 125 + 6 = 131, a prime.
MAPLE
a:=k->`if`(isprime(5^k+2*k), k, NULL): seq(a(k), k=1..5500);
PROG
(GAP) Filtered([1..700], k->IsPrime(5^k+2*k));
(PARI) isok(k) = isprime(5^k + 2*k); \\ Altug Alkan, Apr 19 2018
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Muniru A Asiru, Apr 18 2018
EXTENSIONS
a(11) from Jon E. Schoenfield, Apr 18 2018
STATUS
approved