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A355970 Primes p such that p^2 is the concatenation of x and 2*x+1 for some x. 0
5, 7, 67, 28573, 666667, 31578949, 64912283, 66666667, 666666667, 66666666667, 29083665338647, 31772053083528493, 50819672131147541, 4299928432854102613, 6811594202898550727, 66666666666666666667, 29136816792745854416111, 46823891622677827205227, 66666666666666666666667 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
a(3) = 67 is a term because it is prime and 67^2 = 4489 is the concatenation of 44 and 2*44+1=89.
MAPLE
dcat:=proc(a, b) a*10^(1+ilog10(b))+b end proc:
f:= proc(t) local s;
if not issqr(t) then return NULL fi;
s:=sqrt(t);
if isprime(s) then return s fi
end proc:
map(f, [seq(dcat(x, 2*x+1), x=1..5*10^7)]);
CROSSREFS
Contains A093170.
Sequence in context: A077780 A307361 A260829 * A130189 A180755 A073624
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Jul 21 2022
EXTENSIONS
More terms from Jinyuan Wang, Jul 21 2022
STATUS
approved

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Last modified April 14 13:17 EDT 2024. Contains 371661 sequences. (Running on oeis4.)