The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A138840 Concatenation of initial and final digits of n-th prime. 8
 22, 33, 55, 77, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 11, 13, 17, 19, 13, 17, 11, 17, 19, 19, 11, 17, 13, 17, 13, 19, 11, 11, 13, 17, 19, 21, 23, 27, 29, 23, 29, 21, 21, 27, 23, 29, 21, 27, 21, 23, 23, 37, 31, 33, 37, 31, 37, 37 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS There are only 38 distinct terms in this sequence, all of them odd with the exception of 22. 55 is the only term divisible by 5. 22 and 55 each appear only once. The other terms, each of which appears multiple times, are the odd two-digit numbers not divisible by 5. - Harvey P. Dale, May 15 2012 a(n) is the concatenation of A077648(n) and A007652(n), hence all terms of this sequence have two digits in the same way as A073729. - Omar E. Pol, Mar 23 2018 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 Omar E. Pol, Determinacion geometrica de los numeros primos y perfectos. MAPLE a:= n-> (p-> parse(cat(p[1], p[-1])))(""||(ithprime(n))): seq(a(n), n=1..92); # Alois P. Heinz, Nov 23 2023 MATHEMATICA cifd[n_]:=Module[{il=IntegerLength[n], idn=IntegerDigits[n]}, Which[ il==1, 10n+n, il==2, n, il>2, FromDigits[Join[{First[idn], Last[idn]}]]]]; cifd/@ Prime[ Range[70]] (* Harvey P. Dale, May 15 2012 *) PROG (PARI) a(n) = my(d=digits(prime(n))); fromdigits(concat(d[1], d[#d])); \\ Michel Marcus, Mar 23 2018 CROSSREFS Cf. A000040, A007652, A073729, A077648, A138841, A138842, A138843, A138844. Cf. A137589 (same except for first four terms). Sequence in context: A067287 A026044 A120146 * A257473 A116063 A131317 Adjacent sequences: A138837 A138838 A138839 * A138841 A138842 A138843 KEYWORD base,easy,nonn,look AUTHOR Omar E. Pol, Apr 01 2008 STATUS approved

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

Last modified August 11 05:23 EDT 2024. Contains 375059 sequences. (Running on oeis4.)