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A345314 Primes that can be constructed by concatenating two squares >= 4. 2
449, 499, 1009, 1699, 2549, 4289, 4441, 4729, 6449, 6481, 8419, 9619, 12149, 14449, 16361, 16529, 16729, 16981, 19681, 21169, 22549, 24019, 25121, 25169, 25841, 28099, 28949, 30259, 34819, 36529, 38449, 41521, 41681, 41849, 42209, 43481, 43721, 43969, 45329, 46889 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
If we allow 1, we get sequence A167535.
LINKS
EXAMPLE
449 is a prime that is a concatenation of two squares: 4 and 49.
MAPLE
zcat:= proc(a, b) 10^(1+ilog10(b))*a+b end proc:
select(t -> t <= 10^5 and isprime(t), {seq(seq(zcat(a^2, b^2), a=2..100), b=3..1000, 2)}); # Robert Israel, Jun 17 2021
MATHEMATICA
Take[Select[Union[Flatten[Table[FromDigits[Join[IntegerDigits[n^2], IntegerDigits[k^2]]], {n, 2, 300}, {k, 2, 300}]]], PrimeQ[#] &], 60]
PROG
(Python)
from sympy import isprime
def aupto(lim):
s = list(i**2 for i in range(2, int(lim**(1/2))+2))
t = set(int(str(a)+str(b)) for a in s for b in s)
return sorted(filter(isprime, filter(lambda x: x<=lim, t)))
print(aupto(49000)) # Michael S. Branicky, Jun 13 2021
CROSSREFS
Cf. A167535.
Sequence in context: A071104 A087700 A344827 * A107666 A020466 A142420
KEYWORD
nonn,base
AUTHOR
Tanya Khovanova, Jun 13 2021
STATUS
approved

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Last modified July 12 13:47 EDT 2024. Contains 374247 sequences. (Running on oeis4.)