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A006515 Mersenne numbers with at most 2 prime factors.
(Formerly M2695)
1
3, 7, 31, 127, 2047, 8191, 131071, 524287, 8388607, 2147483647, 137438953471, 2199023255551, 576460752303423487, 2305843009213693951, 147573952589676412927, 9671406556917033397649407, 618970019642690137449562111, 158456325028528675187087900671 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
REFERENCES
John Brillhart, D. H. Lehmer, J. L. Selfridge, Bryant Tuckerman and S. S. Wagstaff, Jr., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
John Brillhart, D. H. Lehmer, J. L. Selfridge, Bryant Tuckerman and S. S. Wagstaff, Jr., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
C. K. Caldwell, Mersenne primes.
S. S. Wagstaff, Jr., The Cunningham Project.
FORMULA
a(n) = A000225(A006514(n)). - Amiram Eldar, Sep 19 2023
MAPLE
A006515 := proc(n) local i;
i := 2^(ithprime(n))-1:
if (nops(numtheory[factorset](i)) < 3) then
return i
fi: end: seq(A006515(n), n=1..19);
MATHEMATICA
Select[Array[2^Prime[#] - 1 &, 25], PrimeOmega@ # <= 2 &] (* Michael De Vlieger, May 04 2017 *)
CROSSREFS
Sequence in context: A105768 A084924 A001348 * A093535 A081093 A057612
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Sean A. Irvine, May 04 2017
STATUS
approved

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Last modified March 19 01:57 EDT 2024. Contains 370952 sequences. (Running on oeis4.)