A095216 - OEIS

A095216

Smallest prime divisor of n-th partial concatenation is prime(n).

2, 1, 5, 11, 27, 81, 153, 91, 71, 183, 27, 67, 147, 219, 347, 99, 831, 109, 627, 329, 1053, 363, 603, 357, 349, 219, 981, 129, 737, 369, 61, 3447, 849, 237, 1281, 693, 719, 691, 851, 19, 2349, 2277, 627, 4163, 3889, 831, 1049, 3973, 1557, 1037, 2943, 1189, 1851

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..53.

EXAMPLE

Smallest prime divisor of 21511 which is a concatenation of first four terms 2,1,5 and 11 is prime(4) = 7, 21511= 7^2*439.

MAPLE

catL := proc(L) local resul, a ; resul := 0 ; for a in L do resul := resul*10^(max(1, ilog10(a)+1))+a ; od ; RETURN(resul) ; end: A020639 := proc(n) op(1, op(1, ifactors(n)[2])) ; end: A095216 := proc(nmax) local a, anext, n; a := [2] ; while nops(a) < nmax do anext := 0 ; n := nops(a)+1 ; while A020639(catL([op(a), anext])) <> ithprime(n) do anext := anext+1 ; od; a := [op(a), anext] ; od ; RETURN(a) ; end: A095216(15) ; # R. J. Mathar, Aug 03 2007

CROSSREFS

Sequence in context: A107310 A277279 A049950 * A307258 A174317 A144237

Adjacent sequences: A095213 A095214 A095215 * A095217 A095218 A095219

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Jun 10 2004

EXTENSIONS

More terms from R. J. Mathar, Aug 03 2007

a(17)-a(53) from Donovan Johnson, May 13 2010

STATUS

approved