A138621 - OEIS

A138621

a(1)=2. For n >=2, a(n) = p(n) *(floor(a(n-1)/p(n)) +2), where p(n) is the n-th prime.

2, 6, 15, 28, 44, 65, 85, 114, 138, 174, 217, 259, 328, 387, 470, 530, 590, 671, 804, 923, 1022, 1106, 1245, 1335, 1455, 1616, 1751, 1926, 2071, 2260, 2413, 2620, 2877, 3058, 3278, 3473, 3768, 4075, 4342, 4671, 5012, 5249, 5539, 5790, 6107, 6368, 6752, 7136

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OFFSET

1,1

COMMENTS

a(n) is the next-to-least multiple of the n-th prime that is > a(n-1).

If we instead had the sequence where a(1)=2 and where a(n) is the least multiple of the n-th prime that is > a(n-1), then a(n) would equal the n-th prime for all positive integers n.

LINKS

Table of n, a(n) for n=1..48.

MAPLE

A138621 := proc(n) option remember ; local a ; if n = 1 then RETURN(2) ; fi ; p := ithprime(n) ; p*(floor(A138621(n-1)/p)+2) ; end: seq(A138621(n), n=1..80) ; # R. J. Mathar, May 20 2008

MATHEMATICA

a = {2}; Do[AppendTo[a, Prime[n]*(Floor[a[[ -1]]/Prime[n]] + 2)], {n, 2, 60}]; a (* Stefan Steinerberger, May 18 2008 *)

nxt[{n_, a_}]:={n+1, Prime[n+1](Floor[a/Prime[n+1]]+2)}; Transpose[NestList[nxt, {1, 2}, 50]][[2]] (* Harvey P. Dale, Mar 18 2013 *)

CROSSREFS

Sequence in context: A192691 A360405 A256313 * A163061 A331773 A033286

Adjacent sequences: A138618 A138619 A138620 * A138622 A138623 A138624

KEYWORD

nonn

AUTHOR

Leroy Quet, May 14 2008

EXTENSIONS

More terms from Stefan Steinerberger and R. J. Mathar, May 18 2008

STATUS

approved