A299382
Numbers k such that k * 19^k - 1 is prime.
Original entry on oeis.org
12, 410, 33890, 91850, 146478, 189620, 280524
Offset: 1
Numbers n such that n * b^n - 1 is prime:
A008864 (b=1),
A002234 (b=2),
A006553 (b=3),
A086661 (b=4),
A059676 (b=5),
A059675 (b=6),
A242200 (b=7),
A242201 (b=8),
A242202 (b=9),
A059671 (b=10),
A299374 (b=11),
A299375 (b=12),
A299376 (b=13),
A299377 (b=14),
A299378 (b=15),
A299379 (b=16),
A299380 (b=17),
A299381 (b=18), this sequence (b=19),
A299383 (b=20).
-
[n: n in [1..10000] |IsPrime(n*19^n-1)];
-
Select[Range[1, 10000], PrimeQ[n*19^n-1] &]
-
for(n=1, 10000, if(isprime(n*19^n-1), print1(n", ")))
A299383
Numbers k such that k * 20^k - 1 is prime.
Original entry on oeis.org
1, 18, 44, 60, 80, 123, 429, 1166, 2065, 8774, 35340, 42968, 50312, 210129
Offset: 1
Numbers n such that n * b^n - 1 is prime:
A008864 (b=1),
A002234 (b=2),
A006553 (b=3),
A086661 (b=4),
A059676 (b=5),
A059675 (b=6),
A242200 (b=7),
A242201 (b=8),
A242202 (b=9),
A059671 (b=10),
A299374 (b=11),
A299375 (b=12),
A299376 (b=13),
A299377 (b=14),
A299378 (b=15),
A299379 (b=16),
A299380 (b=17),
A299381 (b=18),
A299382 (b=19), this sequence (b=20).
-
[n: n in [1..10000] |IsPrime(n*20^n-1)];
-
Select[Range[1, 10000], PrimeQ[n*20^n-1] &]
-
for(n=1, 10000, if(isprime(n*20^n-1), print1(n", ")))
A242338
Numbers k such that k*7^k-1 is semiprime.
Original entry on oeis.org
1, 5, 12, 21, 42, 50, 60, 242, 272
Offset: 1
Cf. similar sequences listed in
A242273.
-
IsSemiprime:=func; [n: n in [2..80] | IsSemiprime(s) where s is n*7^n-1];
-
issemiprime:= proc(n) local F,t;
F:= ifactors(n,easy)[2];
t:= add(f[2],f=F);
if t = 1 then
if type(F[1][1],integer) then return false fi
elif t = 2 then
return not hastype(F,name)
else # t > 2
return false
fi;
F:= ifactors(n)[2];
return evalb(add(f[2],f=F)=2);
end proc:
select(n -> `if`(n::odd, isprime((n*7^n-1)/2),
issemiprime(n*7^n-1)), [$1..100]); # Robert Israel, Aug 19 2014
-
Select[Range[80], PrimeOmega[# 7^# - 1]==2&]
-
for(n=1,100,if(bigomega(n*7^n-1)==2,print1(n,", "))) \\ Derek Orr, Aug 20 2014
Comments