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Complete the recursive formula of the arithmetic sequence 13,6, - 1, - 8, ...

You subtract 7 from the current one to get the next.

f (1) = 13,

f (n) = f (n-1) - 7

Some numbers in the sequence:

f (1) = 13,

f (2) = 6,

f (3) = -1,

f (4) = -8,

f (5) = -15,

f (6) = -22,

f (7) = -29,

f (8) = -36,

f (9) = -43,

f (10) = -50,

f (11) = -57,

f (12) = -64,

f (13) = -71,

f (14) = -78,

f (15) = -85,

f (16) = -92,

f (17) = -99,

f (18) = -106,

f (19) = -113,

f (20) = -120,

f (21) = -127,

f (22) = -134,

f (23) = -141,

f (24) = -148,

f (25) = -155,

f (26) = -162,

f (27) = -169,

f (28) = -176,

f (29) = -183,

f (30) = -190,

f (31) = -197,

f (32) = -204,

f (33) = -211,

f (34) = -218,

f (35) = -225,

f (36) = -232,

f (37) = -239,

f (38) = -246,

f (39) = -253,

f (40) = -260,

f (41) = -267,

f (42) = -274,

f (43) = -281,

f (44) = -288,

f (45) = -295,

f (46) = -302,

f (47) = -309,

f (48) = -316,

f (49) = -323,

f (50) = -330,

f (51) = -337,

f (52) = -344,

f (53) = -351,

f (54) = -358,

f (55) = -365,

f (56) = -372,

f (57) = -379,

f (58) = -386,

f (59) = -393,

f (60) = -400,

f (61) = -407,

f (62) = -414,

f (63) = -421,

f (64) = -428,

f (65) = -435,

f (66) = -442,

f (67) = -449,

f (68) = -456,

f (69) = -463,

f (70) = -470,

f (71) = -477,

f (72) = -484,

f (73) = -491,

f (74) = -498,

f (75) = -505,

f (76) = -512,

f (77) = -519,

f (78) = -526,

f (79) = -533,

f (80) = -540,

f (81) = -547,

f (82) = -554,

f (83) = -561,

f (84) = -568,

f (85) = -575,

f (86) = -582,

f (87) = -589,

f (88) = -596,

f (89) = -603,

f (90) = -610,

f (91) = -617,

f (92) = -624,

f (93) = -631,

f (94) = -638,

f (95) = -645,

f (96) = -652,

f (97) = -659,

f (98) = -666,

f (99) = -673,