A173935 a(n) is the least prime that is the concatenation of two primes in exactly n different ways.

2, 23, 313, 3137, 233347, 739397, 379837313, 73932013313, 7399973479337

Offset

0,1

Links

Table of n, a(n) for n=0..8.

Example

23 = 2 & 3, 313 = 3 & 13 and 31 & 3, etc.

Mathematica

f[n_] := Block[{c = 0, id = IntegerDigits@n, k = 0}, len = Length@ id; While[ k < len, If[ Union@ PrimeQ[ FromDigits@# & /@ {id[[;; k + 1]], id[[k + 2 ;; ]]}] == {True}, c++ ]; k++ ]; c]; t = Table[0, {10}]; p = 2; While[p < 10^8, a = f@p; If[ t[[a]] == 0, t[[a]] = p; Print[{a, p}]]; p = NextPrime@ p]

Crossrefs

Cf. A105184, A106582.

Sequence in context: A294161 A088641 A077203 * A216549 A091693 A276025

Adjacent sequences: A173932 A173933 A173934 * A173936 A173937 A173938

Keyword

base,more,nonn

Author

Robert G. Wilson v, Mar 02 2010

Extensions

a(6) from Robert G. Wilson v, Mar 04 2010

a(7) from Donovan Johnson, Nov 09 2010

a(8) from Giovanni Resta, Mar 04 2014

Status

approved