A343586 - OEIS

A343586

a(n) = the sum of all the multiples of 2 or 5 less than or equal to 10^n.

35, 3050, 300500, 30005000, 3000050000, 300000500000, 30000005000000, 3000000050000000, 300000000500000000, 30000000005000000000, 3000000000050000000000, 300000000000500000000000, 30000000000005000000000000, 3000000000000050000000000000

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..14.

Nicolo Sartori di Borgoricco, Proof that formula is correct

Index entries for linear recurrences with constant coefficients, signature (110,-1000).

FORMULA

a(n) = 3*10^(2*n-1) + 5*10^(n-1).

G.f.: 5*x*(7 - 160*x)/(1 - 110*x + 1000*x^2). - Stefano Spezia, Apr 21 2021

a(n) = 110*a(n-1)-1000*a(n-2). - Wesley Ivan Hurt, Apr 26 2021

EXAMPLE

a(1) = 2 + 5 + 4 + 6 + 8 + 10 = 3*10^(2*1-1) + 5*10^(1-1) = 35.

CROSSREFS

Cf. A065502 (multiples of 2 or 5).

Sequence in context: A290584 A174749 A184124 * A201725 A202578 A213404

Adjacent sequences: A343583 A343584 A343585 * A343587 A343588 A343589

KEYWORD

nonn,easy

AUTHOR

Nicolo Sartori di Borgoricco, Apr 20 2021

STATUS

approved