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A227949
Primes obtained by concatenating decremented numbers starting at a power of 10.
3
109, 10099, 10987, 1000999, 100999897, 10000099999, 1000000999999, 1000999998997, 100000009999999, 10000999999989997, 1000000000999999999, 100999897969594939291, 1000999998997996995994993, 100000000000009999999999999, 10000000000000000000000000099999999999999999999999999
OFFSET
1,1
LINKS
FORMULA
A227949(n) begins with 10^[(A227950(n)-1)/A227951(n)].
EXAMPLE
Since the concatenation of 10 and 9 produces the prime 109, the number 109 is in the sequence.
Since the concatenation of 100 and 99 produces the prime 10099, the number 10099 is in the sequence.
The concatenation of 100, 99, 98 does not produce a prime, hence 1009998 is not in the sequence.
MAPLE
N:= 100: # for terms of up to N digits:
S:= NULL:
for m from 1 to N/2 do
for k from 1 by 2 to 10^m do
x:= parse(cat(seq(i, i=10^m .. 10^m - k, -1)));
if length(x) > N then break fi;
if isprime(x) then S:= S, x; fi
od od:
sort([S]); # Robert Israel, Jan 23 2024
CROSSREFS
KEYWORD
nonn,base
AUTHOR
James G. Merickel, Aug 01 2013
STATUS
approved