OFFSET

0,2

COMMENTS

FORMULA

a(n)=a(n') if respective digits of n and n' differ by 0 or 5. In particular, a(10k+m) = a(10k+m+5) if 0 <= m <= 4.

EXAMPLE

a(16) = 16*16 = 242:

....16

....16

------

....72 (6*6 = 6+6 mod 10 = 2, 6*1 = 6+1 mod 10 = 7)

...27.

------

...242

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PROG

(PARI) A169916(n)={u=vector(#n=digits(n), i, 1); n=apply(d->n+d*u, n)%10; sum(i=0, 2*#n-2, sum(j=max(1, #n-i), min(2*#n-1-i, #n), n[2*#n-i-j][j])%10*10^i)} \\ M. F. Hasler, Mar 26 2015

CROSSREFS

KEYWORD

nonn,base

AUTHOR

STATUS

approved