A238898 Least number m such that lcm(1,2,3,...,m) = lcm(n,n+1,n+2,...,m).

1, 2, 4, 6, 8, 10, 10, 14, 16, 18, 18, 22, 22, 26, 26, 26, 32, 34, 34, 38, 38, 38, 38, 46, 46, 50, 50, 54, 54, 58, 58, 62, 64, 64, 64, 64, 64, 74, 74, 74, 74, 82, 82, 86, 86, 86, 86, 94, 94, 98, 98, 98, 98, 106, 106, 106, 106, 106, 106, 118, 118, 122, 122, 122

Offset

1,2

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 1000 terms from T. D. Noe)

Richard Stong, Twice a Prime Power is Enough (solution to Problem 11761), Amer. Math. Monthly, 123 (2016), pp. 402-403.

Bob Tomper, Problem 11761, Amer. Math. Monthly, 121 (2014), p. 266.

Formula

For n > 1, a(n) = 2*A031218(n-1) [Stong].

Mathematica

Table[m = n; While[LCM @@ Range[m] != LCM @@ Range[n, m], m++]; m, {n, 100}]
f[n_] := If[n < 3, n, m = n - 1; While[ !PrimePowerQ@ m, m--]; 2m]; Array[f, 64] (* Robert G. Wilson v, Mar 06 2018 after Charles R. Greathouse IV *)

Prog

(PARI) a(n)=if(n>2, while(!isprimepower(n--), ); 2*n, n) \\ Charles R Greathouse IV, Jul 10 2015

Crossrefs

Cf. A003418 (LCM), A031218.

Sequence in context: A079431 A081472 A097660 * A176995 A225793 A154809

Adjacent sequences: A238895 A238896 A238897 * A238899 A238900 A238901

Keyword

nonn

Author

T. D. Noe, Mar 13 2014

Status

approved