A167740 Primes that become squares when prefixed with a 7.

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

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

Cf. A167734, A167735, A167736, A167737, A167738, A167739, A167741.

Sequence in context: A020978 A023948 A020974 * A158529 A020766 A069295

Adjacent sequences: A167737 A167738 A167739 * A167741 A167742 A167743

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