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%I #29 Apr 02 2024 14:34:33
%S 2,3,29,31
%N Primes that when squared give numbers with digits in nonascending order.
%C No other solutions below 2*10^9 (probably finite). - Dec 15 1999
%C No other solutions below 10^32. - _David A. Corneth_, Oct 28 2023
%H David A. Corneth, <a href="/A028868/a028868.gp.txt">PARI program</a>
%e From _David A. Corneth_, Oct 28 2023: (Start)
%e 31 is in the sequence as 31 is prime and 31^2 = 961 which has its digits in nonascending order.
%e 2979 is not in the sequence even though 2979^2 = 8874441 does have digits in nonascending order but 2979 = 3^2 * 331 is not prime. (End)
%o (PARI) is(n) = my(d = digits(n^2)); d == vecsort(d,,4) && isprime(n) \\ _David A. Corneth_, Oct 28 2023
%o (PARI) \\ see link for a faster program
%Y Cf. A028869, A028865, A028866.
%K nonn,base,hard,more
%O 1,1
%A _Patrick De Geest_
%E Name clarified by _Jon E. Schoenfield_, Oct 27 2023
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