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A167740 Primes that become squares when prefixed with a 7. 8
29, 569, 1289, 7841, 62129, 306209, 436529, 502121, 634169, 667361, 935489, 1723961, 1927361, 2131049, 2437121, 2539289, 2948681, 3153809, 3564929, 4080449, 5116889, 5846681, 6160529, 6790169, 7316849, 7845329, 8269409, 8481881, 8694641, 8801129, 9869969 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Vincenzo Librandi and David A. Corneth, Table of n, a(n) for n = 1..17124 (first 45 terms from Vincenzo Librandi)
MATHEMATICA
Select[Prime[Range[10000]], IntegerQ[Sqrt[FromDigits[Join[{7}, IntegerDigits[#]]]]]&] (* G. C. Greubel, Jun 23 2016 *)
PROG
(PARI) isok(n) = isprime(n) && issquare(n + 7*10^(length(Str(n)))) \\ Michel Marcus, Aug 05 2013
(PARI)
\\ terms upto 10^n
upto(n) = {my(sqrt71 = sqrt(7.1), sqrt80 = sqrt(8.0), r); for(k=2, n, for(j = ceil((sqrt71 * sqrt(10^k))), floor(sqrt80 * sqrt(10^k)), r = j^2%10^k; if(isprime(r), print1(r", "))))} \\ David A. Corneth, Jun 24 2016
CROSSREFS
Sequence in context: A020978 A023948 A020974 * A158529 A020766 A069295
KEYWORD
base,nonn
AUTHOR
Claudio Meller, Nov 10 2009
EXTENSIONS
More terms from Michel Marcus, Aug 05 2013
Definition modified by Harvey P. Dale, Nov 12 2021
STATUS
approved

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Last modified May 28 22:13 EDT 2024. Contains 372921 sequences. (Running on oeis4.)