A179482 -id:A179482 - cp's OEIS frontend

A009944 Left-right/right-left numbers: n = pq such that n=q_reversed*p_reversed.

126, 153, 688, 187029, 223524, 267034, 1574253, 10013323, 10353244, 36528975, 109019911, 116257833, 1958249722, 2285044524, 2996225824, 6264507888, 10544814252, 15742574253, 31951523916, 35497206387, 62967699976, 94691579179, 182738252812, 187021087029

Offset: 1

Mario Velucchi (mathchess(AT)velucchi.it)

The decimal expansion of n is p followed by q, and n is also the product of R(p)*R(q), where R reverses the order of the digits. - N. J. A. Sloane, May 22 2016
A subset of A179482; only two factors permitted. - Adam Kertesz, Aug 07 2010
The sequence is infinite, since it contains at least 3 infinite subsequences, namely b(n) = 3*(88810 + 2099*10^(6*n))/33670 = 187029, 187021087029,... c(n) = 11011*(1 + 100^(1 + 2*n))/101 = 109019911, 1090198019911,... and d(n) = 3*(53*10000^n - 14900)/10100 = 153, 1574253,... - Giovanni Resta, Mar 17 2013

			E.g. 223524 = 42 * 5322.

Giovanni Resta, Table of n, a(n) for n = 1..30

Cf. A004086, A179482.

Reap[For[n = 1, n < 2*10^8, n++, For[dd = IntegerDigits[n] // Reverse; k = 1, k <= Length[dd] - 1, k++, If[n == FromDigits[dd[[1 ;; k]]]*FromDigits[ dd[[k + 1 ;; -1]]], Print[n]; Sow[n]; Break[]]]]][[2, 1]] (* Jean-François Alcover, May 22 2016 *)

from sympy import divisors
def ok(n):
    if n%10==0: return False
    t = str(n)[::-1]
    return any(t==str(d)+str(n//d) for d in divisors(n, generator=True))
print([k for k in range(10**6) if ok(k)]) # Michael S. Branicky, Apr 13 2024

David W. Wilson has verified that all terms shown are correct, Sep 28 2000

A217247 Numbers that can be obtained by inserting multiplication signs among the digits of their squares.

Original entry on oeis.org

1, 3168, 33696, 322056, 422352, 801792, 3408048, 13304736, 24772608, 26836992, 31959648, 43932456, 98558208, 152845056, 238267008, 250677504, 362330496, 413779968, 511967232, 567502848, 646507008, 1060190208, 1273234464, 1288514304, 1503330304

Offset: 1

Giovanni Resta, Mar 16 2013

The first nontrivial term such that the resulting multiplicands have no leading zeros is given by 152845056^2 = 23361611143643136 and 2*3*3*6*1*6*1*1*14*3*6*4*3*13*6 = 152845056.

			3168 is in the sequence since its square is 10036224 and 1*0036*22*4 = 3168.

Giovanni Resta, Table of n, a(n) for n = 1..55
Giovanni Resta, Decompositions for the first 55 terms

Cf. A179482.

Typo in example corrected by Christian N. K. Anderson, Apr 04 2013

cp's OEIS Frontend

A009944 Left-right/right-left numbers: n = pq such that n=q_reversed*p_reversed.

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