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 A085413 Prime such that concatenation of it and its first digit is prime. 3
 13, 19, 31, 37, 79, 103, 109, 151, 157, 181, 193, 331, 337, 353, 359, 367, 373, 379, 383, 751, 757, 787, 919, 941, 947, 953, 967, 971, 983, 1009, 1021, 1033, 1039, 1063, 1069, 1117, 1201, 1249, 1279, 1291, 1459, 1483, 1489, 1567, 1579, 1597, 1609, 1663, 1669 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Indices of primes in A085412; primes as concatenation of prime and its first digit in A085414. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA Prime[A085412] EXAMPLE 13 is a term because concatenation of 13 and 1 is prime. MAPLE R:= NULL: count:= 0: for d from 1 while count < 100 do for a in [1, 3, 7, 9] do for x from 1 to 10^d-1 by 2 while count < 100 do if isprime(a*10^d + x) and isprime(a*10^(d+1)+10*x+a) then R:= R, a*10^d+x; count:= count+1 fi od od od: R; # Robert Israel, Mar 24 2023 PROG (Python) from itertools import count, islice from sympy import isprime, primerange def agen(): # generator of terms for d in count(1): for f in [1, 3, 7, 9]: for p in primerange(f*10**d, (f+1)*10**d): if isprime(10*p+f): yield p print(list(islice(agen(), 50))) # Michael S. Branicky, Mar 24 2023 CROSSREFS Cf. A085412, A085414. Sequence in context: A040092 A079130 A243587 * A342943 A244311 A358530 Adjacent sequences: A085410 A085411 A085412 * A085414 A085415 A085416 KEYWORD nonn,base AUTHOR Zak Seidov, Jun 29 2003 STATUS approved

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Last modified April 17 07:48 EDT 2024. Contains 371756 sequences. (Running on oeis4.)