A197357 Number of n-digits integers for which the sum of the odd-positioned digits equals the sum of the even-positioned digits.

1, 10, 55, 670, 4840, 55252, 436975, 4816030, 40051495, 432457640, 3715101654, 39581170420, 347847754670, 3671331273480, 32811494188975, 343900019857310, 3113537578058979, 32458256583753952, 296896918816556380, 3081918923741896840

Offset

1,2

Comments

a(n) is the number of n-digit integers such that the sum of the odd-positioned digits is equal to the sum of the even-positioned digits, leading zeros being allowed in the integers.

Links

Colin Barker, Table of n, a(n) for n = 1..200

Example

The number 28754 is one of the 4840 5-digit numbers because 2+7+4 = 8+5.

Prog

(PARI) a(n) = {nb = 0; for (i=0, 10^n-1, digs = digits(i, 10); while(#digs != n, digs = concat(0, digs)); so = 0; forstep(j=1, n, 2, so += digs[j]); se = 0; forstep(j=2, n, 2, se += digs[j]); if (se == so, nb++); ); return (nb); } \\ Michel Marcus, Jun 08 2013

Crossrefs

This sequence has some numbers in common with both A025015 and A174061. In fact, A174061 consists of the elements a(2n), and the elements a(2n) are all elements of A025015.

Sequence in context: A030114 A001557 A367938 * A164951 A244303 A261848

Adjacent sequences: A197354 A197355 A197356 * A197358 A197359 A197360

Keyword

nonn,base

Author

Colin Barker, Oct 13 2011

Status

approved