A069628 a(1) = 1; a(2n) = smallest prime starting (most significant digits) with a(2n-1). a(2n+1) = smallest prime ending (least significant digits) in a(2n).

1, 11, 211, 2111, 22111, 2211109, 92211109, 9221110901, 29221110901, 2922111090137, 32922111090137, 3292211109013747, 73292211109013747, 7329221110901374771, 157329221110901374771, 15732922111090137477101

Offset

1,2

Links

Table of n, a(n) for n=1..16.

Mathematica

a[n_] := (j = ToString[n]; l = {"1", "3", "7", "9", "01", "03", "07", "09"}; k = 1; While[p = ToExpression[ StringJoin[j, ToString[l[[k]] ]]]; k < 9 && ! PrimeQ[p], k++ ]; If[k < 9, Return[p]]; i = IntegerDigits[n]; k = 11; While[p = FromDigits[Join[i, IntegerDigits[k]]]; ! PrimeQ[p], k++ ]; Return[p]); b[n_] := (i = IntegerDigits[n]; k = 1; While[p = FromDigits[ Join[ IntegerDigits[k], i]]; !PrimeQ[p], k++ ]; Return[p]); f[1] = 1; f[n_] := If[ EvenQ[n], a[f[n - 1]], b[f[n - 1]]]; Table[ f[n], {n, 1, 18}]

Crossrefs

Cf. A069614 to A069621, A069628 to A069636.

Sequence in context: A124991 A176009 A068836 * A069613 A075858 A136307

Adjacent sequences: A069625 A069626 A069627 * A069629 A069630 A069631

Keyword

nonn,base

Author

Amarnath Murthy, Mar 27 2002

Extensions

Edited and extended by Robert G. Wilson v, Apr 03 2002

Status

approved