login
A140793
Smallest prime which is the concatenation of 2 or more consecutive numbers starting with n, or -1 if no such prime exists.
5
23, 345678910111213141516171819, 4567, 567891011121314151617, 67, 78910111213, 89
OFFSET
2,1
COMMENTS
Comment from Ray G. Opao, Sep 30 2008: a(9) is the following number:
91011121314151617181920212223242526272829303132333435363738394041424
34445464748495051525354555657585960616263646566676869707172737475767
77879808182838485868788899091929394959697989910010110210310410510610
71081091101111121131141151161171181191201211221231241251261271281291
30131132133134135136137138139140141142143144145146147148149150151152
15315415515615715815916016116216316416516616716816917017117217317417
5176177178179180181182183184185186187.
FORMULA
a(n) = concatenate( n, ..., A084559(n)). - M. F. Hasler, Feb 22 2021
MATHEMATICA
f[n_] := Block[{c = n, k = n + 1}, While[c = 10^IntegerLength[k] c + k; p = c; !PrimeQ[c], k++]; c]; Table[f[n], {n, 2, 8}] (* Robert G. Wilson v, Jun 24 2012 *)
pr[n_]:=Module[{k=1}, While[!PrimeQ[FromDigits[Flatten[IntegerDigits/@Range[n, n+k]]]], k++]; FromDigits[Flatten[IntegerDigits/@Range[n, n+k]]]]; Array[pr, 8, 2] (* Harvey P. Dale, Mar 14 2014 *)
PROG
(PARI) A140793(n, N=n, T=10^logint(n, 10))=while(T*=10, for(m=n+1, n=T-1, ispseudoprime(N=N*T+m)&&return(N))) \\ M. F. Hasler, Feb 22 2021
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Lekraj Beedassy, Jul 15 2008
EXTENSIONS
Added escape clause to definition. - N. J. A. Sloane, Feb 22 2021
STATUS
approved