login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A154522 Numbers n such that number of occurrences of the smallest digit in prime(n) is 2. 1
5, 30, 32, 36, 42, 43, 47, 48, 49, 50, 64, 68, 71, 74, 76, 84, 87, 102, 130, 138, 139, 141, 151, 156, 165, 169, 188, 189, 191, 192, 195, 196, 198, 199, 202, 210, 215, 216, 218, 221, 230, 233, 234, 242, 248, 255, 256, 257, 268, 271, 282, 284, 286, 293, 294, 297 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Indices n such that the smallest digit in prime(n), A060420(n), appears twice in the decimal representation of prime(n). [R. J. Mathar, Jan 12 2009]

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

If 191=prime(n=43), 1=1 and 1<9, the 43=a(6);

If 199=prime(n=45), then 9=9 and 9>1;

If 211=prime(n=47), 1=1 and 1<2, then 47=a(7);

If 223=prime(n=48), 2=2 and 2<3, then 48=a(48), etc.

MAPLE

A060420 := proc(n) convert(ithprime(n), base, 10) ; min(op(%)) ; end: dcount := proc(di, n) local a, d; a := 0 ; convert(n, base, 10) ; for d in % do if d = di then a := a+1 ; fi; od; a ; end: isA154522 := proc(n) local d, c ; d := A060420(n) ; c := dcount(d, ithprime(n)) ; RETURN( c = 2 ) ; end: for n from 1 to 800 do if isA154522(n) then printf("%d, ", n) ; fi; od: # R. J. Mathar, Jan 12 2009

MATHEMATICA

Select[Range[300], Length[Split[Sort[IntegerDigits[Prime[#]]]][[1]]] == 2&] (* Harvey P. Dale, Aug 16 2011 *)

CROSSREFS

Cf. A000040.

Sequence in context: A266569 A098346 A134166 * A253805 A222463 A097252

Adjacent sequences:  A154519 A154520 A154521 * A154523 A154524 A154525

KEYWORD

nonn,base

AUTHOR

Juri-Stepan Gerasimov, Jan 11 2009

EXTENSIONS

Removed 205, 206, 208. Added 210. R. J. Mathar, Jan 12 2009

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)