OFFSET
1,1
LINKS
Pierre CAMI, Table of n, a(n) for n = 1..10000
EXAMPLE
373 is prime so a(1)=3.
MAPLE
q:= n-> isprime(parse(cat(n, 7, n))):
select(q, [ithprime(i)$i=1..500])[]; # Alois P. Heinz, Jun 17 2021
PROG
(PFGW & SCRIPT), the pre10.txt file with the first 10000000 prime numbers.
SCRIPT
DIM i, 0
DIM j
DIM k
DIM n, 1
OPENFILEOUT myf, a(n).txt
OPENFILEIN maf, pre10.txt
GETNEXT j, maf
LABEL loop1
GETNEXT j, maf
IF j>10^n THEN SET n, n+1
SET k, j*10^(n+1)+7*10^n+j
PRP k
IF ISPRP THEN GOTO w
GOTO loop1
LABEL w
SET i, i+1
WRITE myf, j
IF i>9999 THEN END
GOTO loop1
(PARI) lista(nn) = {forprime(p=1, nn, if (isprime(eval(concat(concat(Str(p), 7), Str(p)))), print1(p, ", ")); ); } \\ Michel Marcus, Oct 27 2014
(Magma) [p: p in PrimesUpTo(3000) | IsPrime(Seqint(Intseq(p) cat [7] cat Intseq(p)))]; // Vincenzo Librandi, Oct 27 2014
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Pierre CAMI, Oct 27 2014
STATUS
approved