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URL: https://oeis.org/A028820

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A028820
Squares with digits in nondecreasing order.
6
0, 1, 4, 9, 16, 25, 36, 49, 144, 169, 225, 256, 289, 1156, 1225, 1369, 1444, 4489, 6889, 11236, 11449, 13456, 13689, 27889, 33489, 111556, 112225, 113569, 134689, 146689, 344569, 444889, 2666689, 2778889, 11115556, 11122225, 11135569, 11336689, 11444689, 13446889
OFFSET
1,3
COMMENTS
Number of terms less than 10^k, beginning with k=0: 1, 4, 8, 13, 19, 25, 32, 34, 42, 43, 50, 53, 61, 62, 71, 72, 82, 83, 94, 95, ..., .
Like all squares the ending digits can be 0, 1, 4, 5, 6 or 9. Here is the tally of the list of terms < 10^19: {0, 1}, {1, 1}, {4, 4}, {5, 10}, {6, 13}, {9, 66}. Robert G. Wilson v, Jan 01 2014
LINKS
Robert G. Wilson v and Chai Wah Wu, Table of n, a(n) for n = 1..428 (n = 1..106 from Robert G. Wilson v).
FORMULA
a(n) = A028819(n)^2. - Ray Chandler, Jan 06 2014
MATHEMATICA
Select[Range[0, 4000]^2, Min[Differences[IntegerDigits[#]]]>-1&] (* Harvey P. Dale, Dec 31 2013 *)
Select[Range[0, 10^4]^2, LessEqual@@IntegerDigits[#]&] (* Ray Chandler, Jan 06 2014 *)
PROG
(PARI) mono(n)=n=eval(Vec(Str(n))); for(i=2, #n, if(n[i]<n[i-1], return(0))); 1
for(n=0, 4000, if(mono(n^2), print1(n^2", "))) \\ Charles R Greathouse IV, Aug 22 2011
(Python)
from itertools import combinations_with_replacement
from gmpy2 import is_square
A028820_list = [0] + [n for n in (int(''.join(i)) for l in range(1, 11) for i in combinations_with_replacement('123456789', l)) if is_square(n)] # Chai Wah Wu, Dec 07 2015
CROSSREFS
Intersection of A000290 and A009994.
Sequence in context: A122541 A133743 A235484 * A122683 A235597 A309002
KEYWORD
nonn,base
EXTENSIONS
Definition edited by Zak Seidov, Dec 31 2013
STATUS
approved