login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A245362 Semiprimes such that their reversal + 1 is a square. 1
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 (list; graph; refs; listen; history; text; internal format)
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. Also, reversal(341) + 1 = 143 + 1 = 144 = 12^2.

591 is in the sequence because 591 = 3 * 197, which is semiprime. Also, 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 11 23:04 EDT 2020. Contains 336434 sequences. (Running on oeis4.)