A270542 - OEIS

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A270542

Numbers of the form (pq)^2, where p is the number of digits of n (A055642) and q is the sum of the digits of n (A007953).

0, 1, 2704, 5184, 7744

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OFFSET

1,3

LINKS

Table of n, a(n) for n=1..5.

EXAMPLE

2704 is a term because 2704 = [4*(2+7+0+4)]^2;

5184 is a term because 5184 = [4*(5+1+8+4)]^2.

MATHEMATICA

Position[ Table[ IntegerLength[k] Sum[( Floor[k/10^n] - 10 Floor[k/10^(n + 1)]), {n, 0, IntegerLength@ k^2}] - k, {k, 1, 10^6}], 0] // Flatten = {1, 1232, 4100, 268542}

Select[Range[10^3]^2, With[{id=IntegerDigits[#]}, #==(Length[id]*Plus@@id)^2]&] (* Ray Chandler, Apr 01 2016 *)

PROG

(PARI) isok(n) = d = digits(n); (#d*vecsum(d))^2 == n; \\ Michel Marcus, Mar 26 2016

CROSSREFS

Cf. A007953, A055642, A257784.

Sequence in context: A254506 A254813 A358430 * A250615 A193172 A367668

Adjacent sequences: A270539 A270540 A270541 * A270543 A270544 A270545

KEYWORD

nonn,base,fini,full

AUTHOR

José de Jesús Camacho Medina, Mar 18 2016

STATUS

approved