OFFSET
1,1
COMMENTS
Fermat prime exponents q occur in the case when q = 0, 1, 2, 4, 8, 16.
EXAMPLE
With n = 1, a(1) = 2^0 * 3^0 * 7^0 + 1 = 2.
With n = 5, a(5) = 2^2 * 3^1 * 7^0 + 1 = 13.
list of (q, r, s): (0, 0, 0), (1, 0, 0), (2, 0, 0), (1, 1, 0), (2, 1, 0), (4, 0, 0), (1, 2, 0), (2, 0, 1), (2, 2, 0), (1, 1, 1), ...
MATHEMATICA
With[{n = 19000}, Union@ Select[Flatten@ Table[2^p1*3^p2*7^p4 + 1, {p1, 0, Log[2, n/(1)]}, {p2, 0, Log[3, n/(2^p1)]}, {p4, 0, Log[7, n/(2^p1*3^p2)]}], PrimeQ]] (* Michael De Vlieger, Sep 30 2017 *)
PROG
(GAP)
K:=10^7+1;; # to get all terms <= K.
A:=Filtered([1..K], IsPrime);; I:=[3, 7];;
B:=List(A, i->Elements(Factors(i-1)));;
C:=List([0..Length(I)], j->List(Combinations(I, j), i->Concatenation([2], i)));;
A293008:=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, Sep 28 2017
STATUS
approved