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A078227
a(1) = 2, a(n+1) is the smallest multiple of a(n) such that the digits are alternately odd and even. The unit digit is always even and parity alternates.
4
2, 4, 8, 16, 32, 96, 672, 45696, 2787456, 270383232, 507238943232, 27274745216527872, 141232121898569036783616, 216567470725252501672125832323072
OFFSET
1,1
EXAMPLE
a(7) = 672 = 7*a(6) = 7*96. Starting with the unit digit the digits in 672 are alternately even and odd.
MAPLE
isAltr := proc(n) local nshft, osgn, sgn ; nshft := n ; osgn := ( n mod 10 ) mod 2 ; while nshft >= 10 do nshft := floor(nshft/10) ; sgn := ( nshft mod 10 ) mod 2 ; if sgn = osgn then RETURN(false) ; fi ; osgn := sgn ; od ; RETURN(true) ; end: A078227 := proc(prev) local m; m := 2 ; while true do if isAltr(m*prev) then RETURN(m*prev) ; fi ; m := m+1 ; od ; end: n := 2 : while true do print(n) ; n := A078227(n) : od : # R. J. Mathar, Nov 12 2006
PROG
(Python)
A078227_list = [2]
for _ in range(20):
....x = A078227_list[-1]
....y = x
....while True:
........y += x
........s = str(y)
........for j in range(len(s)-1, -1, -2):
............if not s[j] in ('0', '2', '4', '6', '8'):
................break
........else:
............for k in range(len(s)-2, -1, -2):
................if not s[k] in ('1', '3', '5', '7', '9'):
....................break
............else:
................A078227_list.append(y)
................break
# Chai Wah Wu, Nov 06 2014
KEYWORD
base,more,nonn
AUTHOR
Amarnath Murthy, Nov 23 2002
EXTENSIONS
More terms from R. J. Mathar, Nov 12 2006
a(13) and a(14) from Donovan Johnson, Mar 09 2008
STATUS
approved