OFFSET
1,1
COMMENTS
Mersenne primes A000668 occur when (q, r, s) = (q, 0, 0) with q > 0.
a(2) = 3 is a Mersenne prime but a(3) = 5 is not a Mersenne prime.
For n > 2, all terms = {1, 5} mod 6.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
3 = a(2) = 2^2 * 3^0 * 11^0 - 1.
131 = a(15) = 2^2 * 3^1 * 11^1 - 1.
list of (q, r, s): (0, 1, 0), (2, 0, 0), (1, 1, 0), (3, 0, 0), (2, 1, 0), (1, 2, 0), (3, 1, 0), (5, 0, 0), (2, 0, 1), (4, 1, 0), (1, 3, 0), ...
MAPLE
N:= 10^5: # to get all terms < N
S:=select(isprime, {seq(seq(seq(2^q*3^r*11^s-1, q=0..ilog2(floor(N/3^r/11^s))), r=0..floor(log[3](N/11^s))), s=0..floor(log[11](N)))}):
sort(convert(S, list)); # Robert Israel, Oct 03 2017
MATHEMATICA
With[{nn=20}, Take[Select[Union[Flatten[Table[2^q 3^r 11^s-1, {q, 0, nn}, {r, 0, nn}, {s, 0, nn}]]], PrimeQ], 60]] (* Harvey P. Dale, May 12 2019 *)
PROG
(GAP)
K:=10^5+1;; # to get all terms <= K.
A:=Filtered([1..K], IsPrime);; I:=[3, 11];;
B:=List(A, i->Elements(Factors(i+1)));;
C:=List([0..Length(I)], j->List(Combinations(I, j), i->Concatenation([2], i)));;
A293074:=Concatenation([2], List(Set(Flat(List([1..Length(C)], i->List([1..Length(C[i])], j->Positions(B, C[i][j]))))), i->A[i]));
CROSSREFS
KEYWORD
nonn
AUTHOR
Muniru A Asiru, Oct 01 2017
STATUS
approved