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A074200 a(n) = m, the smallest number such that (m+k)/k is prime for k=1, 2, ..., n. 7
1, 2, 12, 12720, 19440, 5516280, 5516280, 7321991040, 363500177040, 2394196081200, 3163427380990800, 22755817971366480, 3788978012188649280, 2918756139031688155200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Computed by Jack Brennen and Phil Carmody.

LINKS

Table of n, a(n) for n=1..14.

Walter Nissen, Calculation without Words : Doric Columns of Primes.

C. Rivera, Puzzle 181

EXAMPLE

(12+k)/k is prime for k = 1,2,3. 12 is the smallest such number so a(3) = 12.

MATHEMATICA

a[1] = 1; a[n_] := a[n] = For[dm = LCM @@ Range[n]; m = Quotient[a[n - 1], dm]*dm, True, m = m + dm, If[AllTrue[Range[n], PrimeQ[(m + #)/#] &], Return[m]]]; Table[an = a[n]; Print["a(", n, ") = ", an]; an, {n, 1, 10}] (* Jean-Fran├žois Alcover, Dec 01 2016 *)

PROG

(PARI) isok(m, n) = {for (k = 1, n, if ((m+k) % k, return (0), if (! isprime((m+k)/k), return(0))); ); return (1); }

a(n) = {m = 1; while(! isok(m, n), m++); m; } \\ Michel Marcus, Aug 31 2013

(Python)

from sympy import isprime, lcm

def A074200(n):

    a = lcm(range(1, n+1))

    m = a

    while True:

        for k in range(n, 0, -1):

            if not isprime(m//k+1):

                break

        else:

            return m

        m += a # Chai Wah Wu, Feb 27 2019

CROSSREFS

Cf. A078502, A278500.

One less than A093553.

Sequence in context: A007155 A265092 A262032 * A274223 A280734 A048830

Adjacent sequences:  A074197 A074198 A074199 * A074201 A074202 A074203

KEYWORD

nonn,more

AUTHOR

Jean-Christophe Colin (jc-colin(AT)wanadoo.fr), Sep 17 2002, May 10 2010

EXTENSIONS

Corrected by Vladeta Jovovic, Jan 08 2003

a(14) from Jens Kruse Andersen, Feb 15 2004

STATUS

approved

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Last modified April 19 20:04 EDT 2019. Contains 322291 sequences. (Running on oeis4.)