A224473 (2*5^(2^n) - 1) mod 10^n: a sequence of trimorphic numbers ending in 9.

9, 49, 249, 1249, 81249, 781249, 5781249, 25781249, 425781249, 6425781249, 36425781249, 836425781249, 9836425781249, 19836425781249, 519836425781249, 2519836425781249, 12519836425781249, 512519836425781249, 4512519836425781249, 84512519836425781249

Offset: 1

Author

Eric M. Schmidt, Apr 07 2013

Keywords

• nonn
• base

Comments

a(n) is the unique positive integer less than 10^n such that a(n) - 1 is divisible by 2^n and a(n) + 1 is divisible by 5^n.

Links

• Eric M. Schmidt, Table of n, a(n) for n = 1..1000
• Eric Weisstein's World of Mathematics, Trimorphic Number
• Index entries for sequences related to automorphic numbers

Crossrefs

Cf. A033819. Corresponding 10-adic number is A091661. The other trimorphic numbers ending in 9 are included in A002283, A198971 and A224475.

Programs

Sage

def A224473(n) : return crt(1, -1, 2^n, 5^n);

Formula

a(n) = (2 * A007185(n) - 1) mod 10^n.