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A280388
Primes formed from the concatenation of n and previousprime(n).
3
43, 53, 97, 107, 1613, 2423, 3331, 3631, 4241, 4643, 5147, 5347, 5653, 5953, 6361, 6661, 6761, 6967, 7573, 7673, 7873, 8179, 8783, 9689, 102101, 106103, 108107, 111109, 114113, 116113, 123113, 125113, 129127, 130127, 135131, 137131, 144139, 145139, 147139, 148139
OFFSET
1,1
LINKS
EXAMPLE
43 is in the sequence because it is prime formed from the concatenation of 4 and 3, where 3 is largest prime < 4.
1613 is in the sequence because it is prime formed from the concatenation of 16 and 13, where 13 is largest prime < 16.
MAPLE
with(numtheory): select( isprime, [seq((n*10^floor(evalf(log10(prevprime(n))+1, 100))+prevprime(n)), n=3..500)]);
P:=proc(i) local a, n, c; c:=1; for n from 3 by 1 to i do a:=n*10^floor(evalf(log10(prevprime(n))+1, 100))+prevprime(n); if (isprime(a)) then lprint(c, a); c:=c+1; fi; od; end: P(10000);
MATHEMATICA
Select[Table[FromDigits[Join[IntegerDigits[n], IntegerDigits[NextPrime[n, -1]]]], {n, 200}], PrimeQ] (* Harvey P. Dale, Oct 22 2022 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
K. D. Bajpai, Jan 01 2017
STATUS
approved