A280388 Primes formed from the concatenation of n and previousprime(n).

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

K. D. Bajpai, Table of n, a(n) for n = 1..9135

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

Cf. A000040, A084667, A084669, A151799, A151800.

Sequence in context: A306627 A342771 A174818 * A180546 A166491 A127880

Adjacent sequences: A280385 A280386 A280387 * A280389 A280390 A280391

Keyword

nonn,base

Author

K. D. Bajpai, Jan 01 2017

Status

approved