

A195335


Smallest Xmas tree prime with k digits where k is the nth triangular number.


2



2, 211, 211151, 2111511013, 211151101310867, 211151101310867100673, 2111511013108671006731000357, 211151101310867100673100035710000931, 211151101310867100673100035710000931100000213, 2111511013108671006731000357100009311000002131000000901, 211151101310867100673100035710000931100000213100000090110000001797
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OFFSET

1,1


COMMENTS

A Xmas tree prime is a prime which is a concatenation of a prime with a single digit, a prime with two digits, a prime with three digits, a prime with four digits etc. By definition, the number of digits is a triangular number (A000217). Leading zeros are not allowed for any of the primes.


LINKS

Table of n, a(n) for n=1..11.
Terry Trotter, Xmas tree primes


MAPLE

read("transforms") ;
A195335 := proc(n)
option remember;
local prev, nxt, a ;
if n =1 then
2;
else
prev := procname(n1) ;
for nxt from 10^(n1) to 10^n1 do
if isprime(nxt) then
a := digcat2(prev, nxt) ;
if isprime(a) then
return a ;
end if;
end if;
end do:
return 1 ;
end if;
end proc: # R. J. Mathar, Sep 20 2011


CROSSREFS

Cf. A000217.
Sequence in context: A068814 A170920 A215641 * A090560 A181903 A078280
Adjacent sequences: A195332 A195333 A195334 * A195336 A195337 A195338


KEYWORD

nonn,base


AUTHOR

Kausthub Gudipati, Sep 16 2011


STATUS

approved



