A351925 Squares which are the concatenation of two primes.
25, 289, 361, 529, 729, 2401, 2601, 2809, 4761, 5329, 5929, 7569, 11449, 11881, 15129, 19881, 21609, 22801, 23409, 24649, 25281, 26569, 29241, 29929, 31329, 34969, 36481, 39601, 47961, 52441, 53361, 54289, 57121, 58081, 59049, 71289, 77841, 83521, 89401
Offset: 1
Examples
25 is the concatenation of 2 and 5, both primes. 4761 is the concatenation of 47 and 61, both primes.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Maple
L:= NULL: count:=0: for x from 1 by 2 while count < 100 do xs:= x^2; for i from 1 to ilog10(xs) do a:= xs mod 10^i; if a > 10^(i-1) and isprime(a) then b:= (xs-a)/10^i; if isprime(b) then L:= L, xs; count:= count+1; break fi fi od od: L; # Robert Israel, Oct 01 2023 -
PARI
isb(n)={my(d=10); while(d -
Python
from sympy import isprime from itertools import count, islice def agen(): # generator of terms for k in count(1): s = str(k*k) if any(s[i] != '0' and isprime(int(s[:i])) and isprime(int(s[i:])) for i in range(1, len(s))): yield k*k print(list(islice(agen(), 39))) # Michael S. Branicky, Feb 26 2022
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