A245362 Semiprimes whose reversal + 1 is a square.

51, 323, 341, 422, 591, 993, 998, 4227, 4265, 5129, 5534, 5921, 5937, 8049, 8657, 8801, 9953, 32133, 32282, 32471, 32597, 32817, 34091, 34379, 36611, 36863, 38937, 42011, 42243, 42605, 53211, 53673, 55745, 57167, 57903, 59543, 82151, 86354, 86781, 88217, 88433

Offset

1,1

Comments

Semiprimes in A245361.

Similar sequence for primes at A167217.

Links

K. D. Bajpai, Table of n, a(n) for n = 1..1054

Example

341 is in the sequence because 341 = 11 * 31, which is semiprime, and reversal(341) + 1 = 143 + 1 = 144 = 12^2.
591 is in the sequence because 591 = 3 * 197, which is semiprime, and reversal(591) + 1 = 195 + 1 = 196 = 14^2.

Mathematica

Select[Range[10^5], PrimeOmega[#] == 2 && IntegerQ[Sqrt[FromDigits[Reverse[IntegerDigits[#]]] + 1]] &]

Prog

(PARI)
revint(n) = eval(concat(Vecrev(Str(n))))
select(n->bigomega(n)==2 && issquare(revint(n)+1), vector(100000, n, n)) \\ Colin Barker, Jul 20 2014

Crossrefs

Cf. A000290, A001358, A167217, A245361.

Sequence in context: A243462 A251351 A251344 * A219145 A155464 A165087

Adjacent sequences: A245359 A245360 A245361 * A245363 A245364 A245365

Keyword

nonn,base

Author

K. D. Bajpai, Jul 18 2014

Status

approved