A002238 - OEIS

A002238

Numbers k such that 21*2^k - 1 is prime.
(Formerly M0825 N0314)

1, 2, 3, 7, 10, 13, 18, 27, 37, 51, 74, 157, 271, 458, 530, 891, 1723, 1793, 1849, 1986, 2191, 2869, 4993, 7777, 11730, 15313, 29171, 35899, 36227, 71570, 199219, 233914, 297499, 332523, 348547, 538657, 986130, 999599

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

REFERENCES

H. Riesel, Lucasian criteria for the primality of N=h.2^n-1, Math. Comp., 23 (1969), 869-875.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Table of n, a(n) for n=1..38.

Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for k < 300

R. K. Guy, The strong law of small numbers. Amer. Math. Monthly 95 (1988), no. 8, 697-712. [Annotated scanned copy]

Wilfrid Keller, List of primes k.2^n - 1 for k < 300

Kosmaj, Riesel list k<300.

Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

PROG

(PARI) is(n)=ispseudoprime(21*2^n-1) \\ Charles R Greathouse IV, May 22 2017

CROSSREFS

Cf. A032360, 21*2^k + 1 is prime.

Sequence in context: A101956 A273064 A341238 * A002255 A272649 A266813

Adjacent sequences: A002235 A002236 A002237 * A002239 A002240 A002241

KEYWORD

hard,nonn

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Hugo Pfoertner, Jun 22 2004

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

STATUS

approved