A132199 Rowland's prime-generating sequence: first differences of A106108.

1, 1, 1, 5, 3, 1, 1, 1, 1, 11, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 23, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 47, 3, 1, 5, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 101, 3, 1, 1

Offset

1,4

Comments

Rowland shows that the terms are all 1's or primes.

The prime terms form A137613.

See A137613 for additional comments, links and references. - Jonathan Sondow, Aug 14 2008

From Robert G. Wilson v, Apr 30 2009: (Start)

First appearance of k-th prime, k >= 0: 1, 0, 5, 4, 104, 10, 116, 242878, 242819, 22, 243019, 3891770, 242867, ..., .

The number of different numbers in the first 10^k terms beginning with k=0: 1, 4, 7, 12, 15, 19, 30, >35, ..., .

Record high values are A191304. (End)

References

Eric S. Rowland, A simple prime-generating recurrence, Abstracts Amer. Math. Soc., 29 (No. 1, 2008), p. 50 (Abstract 1035-11-986).

Links

Robert G. Wilson v, Table of n, a(n) for n = 1..10000 .

Jean-Paul Delahaye, Déconcertantes conjectures, Pour la Science (French edition of Scientific American), No. 367, May 2008.

Brian Hayes, Pumping the Primes, bit-player, 19 August 2015.

Eric S. Rowland, A natural prime-generating recurrence, arXiv:0710.3217 [math.NT], 2007-2008.

Eric S. Rowland, A simple prime-generating recurrence, 2008.

Eric S. Rowland, Prime-Generating Recurrences and a Tale of Logarithmic Scale, 20 January 2023.

Maple

A106108 := proc(n)
    option remember;
    if n = 1 then
        7;
    else
        procname(n-1)+igcd(n, procname(n-1)) ;
    end if;
end proc:
A132199 := proc(n)
    A106108(n+1)-A106108(n) ;
end proc: # R. J. Mathar, Jul 04 2013

Mathematica

a[1] = 7; a[n_] := a[n] = a[n - 1] + GCD[n, a[n - 1]]; t = Array[a, 104]; Rest@t - Most@t (* Robert G. Wilson v, Apr 30 2009 *)

Prog

(Haskell)
a132199 n = a132199_list !! (n-1)
a132199_list = zipWith (-) (tail a106108_list) a106108_list
-- Reinhard Zumkeller, Nov 15 2013
(PARI)
ub=1000; a=7; n=2; while(n<ub, d=gcd(n, a); print1(d, ", "); a=a+d; n=n+1; ); \\ Daniel Constantin Mayer, Aug 31 2014
(Python)
from itertools import count, islice
from math import gcd
def A132199_gen(): # generator of terms
    a = 7
    for n in count(2):
        yield (b:=gcd(a, n))
        a += b
A132199_list = list(islice(A132199_gen(), 20)) # Chai Wah Wu, Mar 14 2023

Crossrefs

Cf. A106108, A137613, A134734, A134743, A134744, A191304 (record highs) A247090. See A106108 for other cross-references.

Sequence in context: A201654 A265606 A368602 * A111142 A179626 A174965

Adjacent sequences: A132196 A132197 A132198 * A132200 A132201 A132202

Keyword

nonn

Author

N. J. A. Sloane, Jan 28 2008

Status

approved