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A177872 Numbers k such that k is a quadratic residue modulo reverse(k) and reverse(k) is a quadratic residue modulo k. 1
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 15, 22, 29, 33, 37, 38, 40, 44, 47, 51, 55, 56, 65, 66, 73, 74, 77, 78, 79, 83, 87, 88, 90, 92, 97, 99, 100, 101, 110, 111, 113, 117, 121, 124, 125, 131, 141, 143, 144, 146, 149, 151, 161, 163, 164, 167, 169, 171, 174, 181, 187, 189, 191, 198, 202, 209, 212, 222, 226, 232, 242, 252, 262, 263, 266 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..76.

EXAMPLE

a(17) = 38 is in the sequence because L(38/83)) = L(83/38) = 1, where L(a/b) is the Legendre symbol of a and b, which is defined to be 1 if a is a quadratic residue (mod b) and -1 if a is a quadratic non-residue (mod b) .

MAPLE

with(numtheory): for n from 1 to 300 do: s:=0:l:=length(n):for q from 0 to

  l-1 do:x:=iquo(n, 10^q):y:=irem(x, 10):s:=s+y*10^(l-1-q): od: if quadres(n, s)=1

  and quadres(s, n)=1 then printf(`%d, `, n):else fi:od:

CROSSREFS

Sequence in context: A198323 A254649 A261293 * A271839 A290144 A115060

Adjacent sequences:  A177869 A177870 A177871 * A177873 A177874 A177875

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Dec 13 2010

STATUS

approved

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Last modified November 17 05:27 EST 2019. Contains 329217 sequences. (Running on oeis4.)