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!)
A278316 Odd numbers n such that q(n)^2 = q(n^2) != 0, where q(n) is the digit product on base 10. 0
1, 3, 661, 983, 2631, 2893, 12385, 12893, 14661, 18615, 27519, 35383, 36213, 38691, 46215, 49231, 83631, 87291, 92843, 113865, 116683, 123415, 129815, 136423, 139261, 152619, 161683, 162435, 166817, 178119, 194725, 244635, 247941, 254663, 274165, 276941 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

Michael Huke, Solution to exercise psi-15 (German language article), WURZEL 11/2016, November 2016, page 252, http://wurzel.org/

LINKS

Table of n, a(n) for n=1..36.

EXAMPLE

For n=3, a(3)=661: q(661)^2 = (6*6*1)^2 = 36^2 = 1296 = 4*3*6*9*2*1 = q(436921) = q(661^2).

MATHEMATICA

Select[Range[1, 10^6, 2], And[MatchQ @@ #, Times @@ # != 0] &@{(Times @@ IntegerDigits@ #)^2, Times @@ IntegerDigits[#^2]} &] (* Michael De Vlieger, Dec 06 2016 *)

PROG

(PARI) pd(n) = my(d=digits(n)); prod(k=1, #d, d[k]);

isok(n) = (n % 2) && (p = pd(n)^2) && (p == pd(n^2)); \\ Michel Marcus, Dec 04 2016

CROSSREFS

Odd terms of A256115. - Michel Marcus, Dec 04 2016

Sequence in context: A092301 A229668 A165343 * A266639 A203496 A308323

Adjacent sequences:  A278313 A278314 A278315 * A278317 A278318 A278319

KEYWORD

nonn,base

AUTHOR

Volker Diels-Grabsch, Nov 18 2016

EXTENSIONS

More terms from Jon E. Schoenfield, Dec 02 2016

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 February 18 12:34 EST 2020. Contains 332018 sequences. (Running on oeis4.)