

A138840


Concatenation of initial and final digits of nth 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
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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 twodigit numbers not divisible by 5.  Harvey P. Dale, May 15 2012


LINKS



MAPLE

a:= n> (p> parse(cat(p[1], p[1])))(""(ithprime(n))):


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. A137589 (same except for first four terms).


KEYWORD



AUTHOR



STATUS

approved



