A078228 a(n) = A078227(n+1)/A078227(n).
2, 2, 2, 2, 3, 7, 68, 61, 97, 1876, 53771, 5178128, 1533415117
Offset: 1
Extensions
a(8)-a(13) from Donovan Johnson, Nov 11 2008
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(6) = 567 = 7*a(5); the digits alternate odd, even, odd.
isA030141 := proc(n) local dgs,i ; dgs := convert(n,base,10) ; for i from 1 to nops(dgs)-1 do if ( op(i,dgs)+op(i+1,dgs)) mod 2 = 0 then RETURN(false) ; fi ; od ; RETURN(true) ; end: A078226 := proc(nmax) local a,f; a := [1] ; while nops(a) < nmax do f := 3 ; while true do if isA030141(f*op(-1,a)) then a := [op(a),f*op(-1,a)] ; print(op(-1,a)) ; break ; fi ; f := f+2 ; od ; od ; end: A078226(13) ; # R. J. Mathar, Mar 01 2007
A078226_list = [1] for _ in range(20): x = A078226_list[-1] y, x2 = x, 2*x while True: y += x2 s = str(y) for j in range(len(s)-1, -1, -2): if not s[j] in ('1', '3', '5', '7', '9'): break else: for k in range(len(s)-2, -1, -2): if not s[k] in ('0', '2', '4', '6', '8'): break else: A078226_list.append(y) break # Chai Wah Wu, Nov 06 2014