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A031974 1 repeated prime(n) times. 18
11, 111, 11111, 1111111, 11111111111, 1111111111111, 11111111111111111, 1111111111111111111, 11111111111111111111111, 11111111111111111111111111111, 1111111111111111111111111111111, 1111111111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Salomaa's first example of an infinite language. - N. J. A. Sloane, Dec 05 2012

If p is a prime and gcd(p,b-1)=1, then (b^p-1)/(b-1) == 1 (mod p); by Fermat's little theorem. For example 1111111 == 1 (mod 7). - Thomas Ordowski, Apr 09 2016

REFERENCES

A. Salomaa, Jewels of Formal Language Theory. Computer Science Press, Rockville, MD, 1981, p. 2. - From N. J. A. Sloane, Dec 05 2012

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..50

Fanel Iacobescu, Smarandache Partition Type Sequences, in Bulletin of Pure and Applied Sciences, India, Vol. 16E, No. 2, 1997, pp. 237-240

M. Le and K. Wu, The Primes in the Smarandache Unary Sequence, Smarandache Notions Journal, Vol. 9, No. 1-2. 1998, 98-99.

Eric Weisstein's World of Mathematics, Smarandache Sequences

FORMULA

a(n) = A000042(A000040(n)). - Jason Kimberley, Dec 19 2012

a(n) = (10^prime(n) - 1)/9. - Vincenzo Librandi, May 29 2014

MAPLE

f:=n->(10^ithprime(n)-1)/9; [seq(f(n), n=1..20)]; # N. J. A. Sloane, Dec 05 2012

MATHEMATICA

Table[FromDigits[PadRight[{}, Prime[n], 1]], {n, 15}] (* Harvey P. Dale, Apr 10 2012 *)

PROG

(MAGMA) [(10^p-1)/9: p in PrimesUpTo(40)]; // Vincenzo Librandi, May 29 2014

CROSSREFS

A004022 is the subsequence of primes. - Jeppe Stig Nielsen, Sep 14 2014

Sequence in context: A136982 A083441 A261269 * A117293 A015468 A037842

Adjacent sequences:  A031971 A031972 A031973 * A031975 A031976 A031977

KEYWORD

nonn,easy,base

AUTHOR

J. Castillo (arp(AT)cia-g.com) [Broken email address?]

EXTENSIONS

More terms from Erich Friedman

Corrected and extended by Harvey P. Dale, Apr 10 2012

STATUS

approved

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Last modified May 26 17:40 EDT 2020. Contains 334630 sequences. (Running on oeis4.)