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A038692 Square numbers that are concatenations of two or more prime numbers. 6

%I #16 Mar 16 2020 09:10:32

%S 25,225,289,361,529,729,2401,2601,2809,4761,5329,5929,7225,7569,11449,

%T 11881,13225,15129,19881,21609,22801,23409,24649,25281,26569,27225,

%U 29241,29929,31329,32761,34969,36481,39601,47961,52441,53361,54289,55225,57121,58081

%N Square numbers that are concatenations of two or more prime numbers.

%H Jinyuan Wang, <a href="/A038692/b038692.txt">Table of n, a(n) for n = 1..1000</a>

%F A038692(n) = A166503(n)^2. As a set, A038692 = A000290 intersection A152242 = A016754 intersection A152242. - _M. F. Hasler_, Mar 19 2012

%t ric[d_] := PrimeQ@ FromDigits@ d || AnyTrue[ TakeDrop[d, #] & /@ Range[ Length[d] - 1], #[[2,1]] > 0 && PrimeQ@ FromDigits@ #[[1]] && ric@ #[[2]] &]; ok[n_] := If[ EvenQ[n] && Mod[n, 10] != 2, False, ric@ IntegerDigits@ n]; Select[ Range[300]^2, ok] (* _Giovanni Resta_, Mar 16 2020 *)

%o (PARI) forstep(n=1, 300, 2, is_A152242(n^2) & print1(n^2, ", ")) \\ _M. F. Hasler_, Mar 19 2012

%Y Cf. A166503 (the square roots).

%K nonn,base

%O 1,1

%A _Jeff Burch_

%E Edited by _N. J. A. Sloane_, Oct 18 2009, incorporating corrections from _M. F. Hasler_ and Zak Seidov.

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)